People gather atop the aircraft steps at a Syrian passenger plane that was forced by Turkish jets to land at Esenboga airport in Ankara, Turkey, Wednesday, Oct. 10, 2012. (Burhan Ozbilici/AP)

Turkey claimed Thursday that it had found Russian munitions aboard a Syrian passenger jet forced to land in its capital, Ankara, drawing Moscow into the spiraling Syrian-Turkish tensions that are threatening to erupt into regional war.

Russia demanded an explanation from Turkey for the interception of the Syrian Air plane, which was escorted to the civilian airport in Ankara by Turkish F-16s on Wednesday and detained for nearly eight hours before being allowed to continue on its way without its cargo.

At a news conference Thursday evening, Turkish Prime Minister Recep Tayyip Erdogan said that the cargo included unspecified “munitions,” adding that an investigation was continuing.

“This was munitions from the Russian equivalent of our Mechanical and Chemical Industry Corporation being sent to the Syrian Defense Ministry,” Erdogan told reporters in Ankara, in a reference to the state-run manufacturer that supplies Turkey’s military.

Turkish news reports indicated that the equipment included electronic communications devices, but a Turkish official who spoke on the condition of anonymity because of the sensitivity of the subject declined to elaborate on what exactly was found, other than to describe it as “military equipment.”

Syria denied that there was any improper cargo aboard the plane and accused Turkey of an act of “air piracy.” All the items on board the plane had been properly registered, Syria’s Foreign Ministry said in a statement. “The cargo did not include any types of weapons or prohibited goods,” it said.

The interception followed a week of sky-high tensions between Syria and Turkey that began with the deaths of five civilians in a Syrian mortar strike against a Turkish village. Turkey fired back, triggering five days of mortar exchanges that raised fears that a full-blown war could be imminent.

Although the artillery fire has ceased, the interception of the Airbus plane points to Turkey’s growing frustration with the crisis unfolding along its borders as Syrian government forces battle rebels seeking to topple President Bashar al-Assad. Turkey has been inundated with nearly 100,000 Syrian refugees fleeing the violence, and stray shells had crashed into the Turkish side of the border several times in recent months, without causing casualties.

Turkish officials suspect, however, that though those earlier strikes apparently involved errant shells fired by Assad’s security forces struggling to hold ground against rebel advances across northern Syria, last week’s deadly strike was different because six shells fired simultaneously landed in the same village, and the mortar rounds continued even after Turkey retaliated.

Erdogan criticized at home

Meanwhile, Erdogan’s government has come under growing domestic criticism for a policy that has aggressively supported the Syrian opposition without demonstrating any discernible benefit for Turkey or, seemingly, accelerating Assad’s departure.

“Turkey’s Syria policy is on the verge of proving to be a complete fiasco,” columnist Emre Uslu wrote in the Today’s Zaman newspaper last week.

Turkey has hosted the leadership of the opposition Free Syrian Army in a camp near the border and has allowed rebel fighters to freely traverse its borders with weapons and funds. It has also called for a no-fly zone in northern Syria, similar to the one imposed over Libya last year, to provide a haven for refugees, deter them from entering Turkey and protect rebel gains in the area.

The Free Syrian Army continues to make advances, albeit slowly, against government forces in the north, and this week it claimed to have captured the key town of Maarat al-Numan in the northern province of Idlib. Battles are continuing there, but if the rebels prevail, they will have severed a vital supply route between the capital, Damascus, and the city of Aleppo, a strategic prize in the rebel effort to carve out a swath of liberated territory.

Yet Turkey’s NATO allies have shown little appetite for any form of military intervention in volatile Syria, despite repeated assertions of support for Turkey and strenuous calls for Assad to depart. And Assad clings to power in Damascus despite nearly 19 months of increasingly violent challenges to his rule, shored up by the unwavering support of Russia, Iran, the Shiite Hezbollah-led government in Lebanon and the Shiite-led government in Iraq.

In a reminder of the risk that the tensions emanating from the Syria crisis could provoke a regional conflagration, Hezbollah leader Hasan Nasrallah asserted responsibility for dispatching a spy drone over Israel that was shot down by Israeli jets on Saturday. “This was not the first time and will not be the last,” he said in a televised address broadcast in Lebanon on Thursday night.

It was, however, the first time that such a drone has penetrated Israeli airspace since 2006, when Israel and Hezbollah fought a brief, bloody but inconclusive war that many Lebanese fear could recur as the region polarizes over the Syria crisis. Israel said it was considering its response.

Interception angers Kremlin

Russia responded angrily to the challenge to the Syrian flight, which departed from Moscow, saying Turkey had endangered the lives of 17 Russians among the about 30 passengers aboard.

“Russia insists that the Turkish authorities explain their conduct regarding Russian citizens and prevent similar incidents in the future,” Russian Foreign Ministry spokesman Alexander Lukashevich said Thursday. His statement did not address the contents of the cargo seized aboard the plane.

Russia does not deny that it is supplying weapons to Assad’s government, but it also routinely notes that such supplies are not forbidden under international law. Russia, along with China, has repeatedly blocked efforts at the United Nations to impose tougher sanctions against Syria that would prohibit arms transfers.

“Russia has delivered weapons — and this happened on the basis of long-existing contracts — to the legitimate, internationally recognized government of Syria,” Vladimir Yakunin, an aide to Russian President Vladimir Putin, said in an interview Thursday with Germany’s Der Spiegel.

In Washington, State Department spokeswoman Victoria Nuland said that the United States supports Turkey’s decision to inspect the plane but that she did not have details about what was found.

“We would be concerned by any effort to supply military equipment to the Assad regime because it’s clearly being used by the regime against their own people,” she said.

Will Englund in Moscow and Ahmed Ramadan in Beirut contributed to this report.

by Liz Sly

BEIRUT — Russia demanded an explanation from Turkey on Thursday for why it intercepted a Syrian passenger plane flying from Moscow to Damascus, the latest instance of spiraling Syrian-Turkish tensions related to Syria’s bloody civil war.

Turkey said it used F-16 fighter jets to force the Syrian Airbus to land at Esenboga Airport in Ankara in order to seize equipment that it believes was destined for use by the Syrian military against the armed, anti-government rebels.

Syrian Transport Minister Mahmoud Said said the move amounted to “air piracy,” Reuters quoted the state-controlled television news as saying. The comments exacerbated the already tense back-and-forth between Turkey and Syria following a Syrian mortar strike that killed five civilians in a Turkish border village last week.

The Airbus 320, with 30 passengers on board, was intercepted as it entered Turkish airspace shortly after 5 p.m. local time on Wednesday (10 a.m. in Washington). Hours earlier, Turkey had ordered all Turkish civilian aircraft to cease flights through Syrian airspace, apparently to prevent Syria from taking reciprocal action.

Turkish Foreign Minister Ahmet Davutoglu told Turkish television network TGRT that the plane had been forced down because it was carrying “non-civilian cargo” and “banned material.”

“There is information that the plane had cargo on board that does not meet the requirements of civil aviation,” Davutoglu said. The Today’s Zaman newspaper later reported that Turkish authorities found military communication equipment and “parts that could be used in missiles” on the plane.

Russia denied that any military hardware or weapons were on board.

In Brussels, meanwhile, U.S. Defense Secretary Leon Panetta told reporters the United States has dispatched a small force of 150 troops to Jordan, to help the authorities there formulate contingency plans for dealign with the ongoing violence in neighboring Syria.

Russia demands explanation

Russia’s Foreign Ministry said Turkey never informed the Russian embassy that 17 Russians were on board the seized plane. After learning about it from news reports, the embassy sent consulate workers and a doctor to the airport, spokesman Alexander Lukashevich said, and demanded access to the Russians.

“Russia insists that the Turkish authorities must explain their conduct regarding Russian citizens and prevent similar incidents in the future,” Lukashevich said in a statement.

“Turkish authorities denied without explanations and in violation of the bilateral consular convention a meeting of the diplomats with the Russian citizens, who had been barred from the airport terminal for eight hours but sporadically allowed to stand on the tarmac,” Lukashevich said.“No food was supplied either.”

The Interfax news agency quoted an unnamed official with a “Russian weapons export organization” as saying that there were no weapons or military hardware on board the plane. The official pointed out that Russia has not suspended military-technological cooperation with Syria, and therefore could send weapons to Damascus through official channels, rather than trying to smuggle such material on a civilian plane.

“If it had been necessary to ship any military hardware or weapons to Syria, this would have been done through the established procedure rather than in an illegal way, not to mention using a civilian aircraft,” the official said, according to Interfax.

Russia, one of Syria’s staunchest allies, has in the past acknowledged supplying the government in Damascus with weapons and has blocked several efforts at the United Nations to impose an arms embargo.

Conflict escalates

Ankara and Damascus, long at odds over the bloody revolution in Syria, lurched closer to war a week ago after several Syrian shells exploded in a Turkish border village, killing five civilians and prompting Turkey to retaliate with barrages of mortar fire against Syrian targets.

Syria refused to apologize and instead denounced Turkey for allowing rebels battling the regime led by President Bashar al-Assad to transport weapons and funds across its border. Although mortar rounds fired during battles had strayed into Turkey on several previous occasions, Turkish officials said the incident last week was different because five shells struck a residential area almost simultaneously.

Over the next five days, at least five more Syrian shells exploded in Turkey, increasing suspicions that Syria was deliberately needling its neighbor in an effort to undermine Turkish Prime Minister Recep Tayyip Erdogan. Turkey reciprocated by firing mortar shells into Syria on each occasion, and it has reinforced its southern border with extra troops, artillery and fighter planes.

Earlier Wednesday, Turkey’s top general warned of harsher retaliation if more Syrian mortar shells land in Turkish territory.

“We responded, but if it continues, we will respond with greater force,” Chief of General Staff Necdet Ozel told Turkish media during a visit to the southern town of Akcakale, where the five civilians were killed.

The dispatch of the U.S. troops to Jordan, reported by the New York Times on Wednesday, marks the first American military deployment directly associated with the nearly 19-month-old Syria crisis, which has swamped neighboring states with refugees and risks igniting a regional conflict. The Local Coordination Committees, an opposition group, said 173 people were killed in Syria on Wednesday.

Most of the 150 U.S. troops are Army special operations forces, and some have been in Jordan for several months, Panetta said. They are helping Jordan monitor Syrian chemical and biological weapons sites and develop its own military capabilities “so that we can deal with all of the possible consequences” of the Syria war, he said.

Will Englund contributed to this report.