An Israeli air force F-15 Eagle jet fighter plane takes off from Tel Nof air force base for a mission over Gaza Strip in central Israel, Monday, Nov. 19, 2012. (AP Photo/Ariel Schalit) (Ariel Schalit/AP)

Israeli aircraft struck inside Syria on Wednesday for the first time since 2007, according to Western and Syrian officials, in a development that underlined the risk that the civil war in Syria could spill over into a wider conflict.

There were conflicting reports about the target and its location. A Western official and a former Lebanese security official said earlier Wednesday that Israel had attacked inside Syria along the border with Lebanon, and the former Lebanese official said an unmanned aircraft had hit a truck carrying weapons. But in a later statement, the Syrian army denied a strike along the border and said instead that Israeli jets had bombed a defense research center near Damascus.

Israel declined to comment, as did U.S. officials, who deferred to Israel, a key security partner. The response was similar to the silence that followed Israel’s bombing five years ago of a suspected Syrian nuclear reactor, an attack that U.S. officials later confirmed but that the Israelis have not acknowledged to date.

The attack Wednesday highlighted deepening Israeli concerns that the disintegration of Syria could lead to the transfer of advanced weapons to Islamist militants there or to the Iranian-backed Hezbollah militant group in neighboring Lebanon, posing new threats to Israel’s military reach across its borders.

Hezbollah, which is closely aligned with both Syria and Iran, condemned the airstrike as “barbaric aggression” and expressed “full solidarity with Syria’s command, army and people,” the Associated Press reported. Russia, Syria’s chief patron, said the strike would constitute “unprovoked attacks on targets on the territory of a sovereign country, which blatantly violates the U.N. Charter and is unacceptable, no matter the motives to justify it.”

Timeline: Major events in Syria’s tumultuous uprising that began in March 2011.

The Syrian government said in a statement that Israeli aircraft had bombed “a scientific research center responsible for raising the levels of resistance and self-
defense” in Jamraya, northwest of Damascus, the capital.

The statement said the Israeli planes had flown below radar range and destroyed the building, killing two employees and wounding five. The statement denied that a convoy had been hit near the border with Lebanon, calling the reports “baseless.”

But according to earlier accounts by the Western official and a U.S. official, Israeli aircraft struck near the Syria-Lebanon border. The officials said there were no indications that chemical weapons were targeted.

Concerns about Hezbollah

The Associated Press, citing unnamed regional security officials, said that Israel had been planning to target a Syrian shipment of antiaircraft missiles bound for Hezbollah and that the shipment included sophisticated Russian-made SA-17 missiles.

Although Israeli and U.S. security officials have said that Syria’s chemical weapons stockpiles were secure for now, there is profound concern in Israel about a parallel transfer of advanced conventional weapons to Hezbollah.

Giora Eiland, a former head of Israel’s national security council, said in an interview that any transfer to Hezbollah of weapons considered to be game-changers, such as the Russian antiaircraft missiles or long-range Scud missiles, is viewed as gravely as the chemical threat.

The antiaircraft weapons could curtail Israel’s air dominance in Lebanon, and the long-range missiles could give Hezbollah — which fought a war with Israel in 2006 — enhanced strike range across Israel’s entire territory.

“These are no less troubling than chemical weapons,” Eiland said. “They are more widespread and not as tightly controlled by the regime, so they can fall into the hands of Hezbollah.”

Earlier Wednesday, Lebanon’s military said 12 Israeli warplanes had violated Lebanese airspace in less than 24 hours, flying low in several sorties over villages in southern Lebanon.

The Israeli army said it would not comment on the reports, which followed several days of statements and high-level consultations on Syria among senior Israeli officials.

On Sunday, Israeli Vice Prime Minister Silvan Shalom told Army Radio that the movement of chemical weapons to Islamist rebels in Syria or to Hezbollah would be “a crossing of all red lines that would require a different approach, including even preventive operations.” He confirmed media reports that Prime Minister Benjamin Netanyahu had convened a meeting of top security chiefs last week to discuss developments in Syria and its chemical arsenal.

In public comments Sunday at the start of the weekly cabinet session, Netanyahu said Israel had to keep an eye on “lethal weaponry in Syria, which is breaking apart.” He added that there is “an accumulation of threats” for which Israel has to prepare.

Two Iron Dome missile defense batteries were positioned Sunday in northern Israel, in what the army called part of a routine rotation nationwide.

Many regional analysts say Hezbollah has not only restocked its weapons arsenal since the 2006 war but has also greatly expanded the supply and sophistication of its rockets. In a speech in May 2012, Hasan Nasrallah, the group’s leader, said Hezbollah could now launch rockets anywhere in Israel, and he later remarked that Syria had supplied the group’s most potent weapons.

Amnon Sofrin, a former director of intelligence for Israel’s foreign spy agency, the Mossad, told reporters in Jerusalem on Wednesday that with Syria in turmoil, Nasrallah was eager “to move to Lebanon everything he can under his custody.” Sofrin said Israel was watching carefully for convoys of weapons moving to Lebanon from Syria, where Hezbollah is thought to have stored some of its arms.

Mystery about motives

The Syrian assertion that Israel had bombed a research center deepened the mystery surrounding the possible motives for the attack. The official statement suggested that the target might have been a facility near Damascus operated by the Scientific Studies and Research Center, an arm of Syria’s armed forces that Western experts have linked to the country’s missiles and chemical weapons programs.

In 2005, the George W. Bush administration sanctioned the SSRC in an executive order, and two years later, the White House froze the assets of several of the center’s subsidiaries, on the grounds that SSRC scientists were seeking to develop “non-conventional weapons and the missiles to deliver them.”

Yet, military experts cautioned that there was no independent evidence that the facility had been bombed by a foreign air force. Syria may simply be trying to blame Israel for the loss of a facility that had fallen to rebels or been destroyed by other means, said Anthony Cordesman, a senior analyst at the Center for Strategic and International Studies, a Washington think tank.

“Would the Israelis have hit a facility that may have some chemical weapons in it? It’s doubtful,” said Cordesman, who co-authored a 2008 study of Syria’s weapons program. “If they did, Syria could respond by dispersing its arsenal further, which would increase the risk to Israel.”

On Wednesday morning, the Britain-based Syrian Observatory for Human Rights released a list of security incidents that included reports of shelling and a “huge fire” in the Jamraya area.

Rami Abdulrahman, who is the director of the monitoring group and who uses a pseudonym, said in an interview that reports about the incident were conflicting, with some local sources saying that it involved mortar shells and others alleging that Syrian airplanes struck the building.

Greenberg reported from Jerusalem. Joby Warrick, Julie Tate, Karen DeYoung and Anne Gearan in Washington contributed to this report.