Israeli warplanes bombed the outskirts of Damascus early Sunday for the second time in recent days, according to Syrian state media and reports from activists, signaling a sharp escalation in tensions between the neighboring countries that had already been exacerbated by the conflict raging in Syria.

Though there was no official confirmation that Israel had carried out the attack, the Israeli military later announced that it had deployed two of its Iron Dome rocket defense batteries near its northern border in response to what it called “ongoing situational assessments.”

Videos posted on the Internet by activists showed a huge fireball erupting on Mount Qassioun, a landmark hill overlooking the capital on which the Syrian government has deployed much of the firepower it is using against rebel-controlled areas surrounding the city.

The official Syrian Arab News Agency said that a scientific research facility had been struck by an Israeli missile, and a banner displayed on state television said the attack was intended to relieve pressure on rebel forces in the embattled eastern suburbs. The banner was accompanied by martial music and footage of Syrian soldiers marching, descending from helicopters and firing rockets, indicating that Syria may not shrug off the assault, as it has with some Israeli strikes in the past.

Reuters reported that an Israeli military spokeswoman had refused to comment, but the Associated Press quoted an anonymous Middle East intelligence official as confirming the state media reports. The target was Fateh-110 missiles, which have precision guidance systems with better aim than anything Hezbollah is known to have in its arsenal, the official said.

A subsequent video posted on the Internet by activists showed further multiple explosions lighting up the skies over Damascus, suggesting that some form of arms storage facility may have been hit.

Syria’s Foreign Ministry said Sunday that Israel had intervened on behalf of the rebels.

“The Israeli attack on military sites in Syria is proof that there is communication between Israel and the terrorist groups who take their orders from al-Qaeda,” the ministry said in a statement published on Syrian state television.

The network said the Syrian Cabinet would convene an emergency meeting to discuss the attack.

The attack Sunday came hours after U.S., Israeli and Lebanese officials said Israeli warplanes on Friday had struck a shipment of missiles destined for Lebanon’s Hezbollah movement at Damascus International Airport.

The attacks coincided with mounting pressure on the Obama administration to formulate a response to the growing risk of weapons proliferation in the Syrian war, notably the possibility that chemical weapons are being used in the conflict and could fall into the hands of extremists.

It also came amid renewed reports of sectarian violence in the northern coastal region of Latakia, a stronghold of Syrian President Bashar al-Assad where his supporters allegedly killed at least 50 and perhaps as many as 100 Sunni Muslim villagers in recent days, drawing a sharp condemnation Saturday from the State Department.

Israeli officials told the Associated Press and Reuters that the target of the Friday airstrike was a consignment of advanced, long-range, ground-to-ground missiles destined for Hezbollah, the political and military organization that dominates Lebanon’s government and has been designated a terrorist organization by the United States.

The shipment did not contain chemical weapons, but the missiles were potentially “game-changing,” one official told the Associated Press.

A Shiite Lebanese analyst with close ties to Hezbollah said late last month that the war in Syria has failed to slow the movement of arms and other resources to Hezbollah.

“[Hezbollah] still has it coming in from Syria because Damascus is still controlled by the Syrian army, and the airport is theirs,” Mohammed Obeid said in an interview.

Obeid said he communicates with Hezbollah leaders on a daily basis and frequently meets with Syrian officials in Damascus.

Details of that attack were sketchy, but it appeared the target was a storage site at an air defense base on the periphery of the Damascus airport, known to be the chief transshipment point for weapons flown into Syria from Iran, both to aid the Syrian government in its battle against rebels and to supply Iran’s ally Hezbollah in Lebanon.

A senior Lebanese security official who was in Damascus at the time said the strike took place about 4 a.m. and targeted a large quantity of missiles stored at the site. The official, who, like the others, spoke on the condition of anonymity because of the sensitivity of the subject, did not know the origin or the destination of the missiles.

There were reports Friday that an overnight rebel mortar attack had caused a huge blaze at the Damascus airport, with a video posted online showing at least two locations on fire. But the Lebanese security official said that the blasts, which woke him up, were bigger than those caused by mortar shells and that his Syrian counterparts had confirmed to him that the source was an Israeli strike.

The attack appeared to be similar to one in January in which Israeli jets hit a convoy carrying weapons intended for Hezbollah, the official said, with the warplanes firing from a location over Lebanon’s Bekaa Valley.

His claims could not be independently confirmed, but a Syrian opposition Web site also said that the Damascus airport was the target, according to Israel’s Haaretz newspaper. Lebanese authorities and residents had reported unusually intense Israeli overflights during the previous 48 hours, suggesting that the warplanes may have struck their target from Lebanese airspace.

A U.S. official in Washington confirmed that the strike had taken place but refused to provide details. Spokesmen for Israeli Prime Minister Benjamin Netanyahu and the Israel Defense Forces declined to comment on the reports.

Israel has also not officially confirmed that it carried out the January strike, on a convoy reportedly transporting antiaircraft missiles to Hezbollah, and the fact that some officials swiftly acknowledged U.S. reports of this attack pointed to Israel’s growing determination to directly confront the threat posed by the Syrian conflict.

Netanyahu and military and intelligence commanders in Israel have repeatedly warned that they will not tolerate the transfer of sophisticated weaponry to Hezbollah under cover of the turmoil of the Syrian war, and they have also expressed certainty in recent weeks that Assad has used chemical weapons in at least two small-scale attacks. One concern is that Syria and Iran will supply Hezbollah with a chemical-weapons capability.

But there are also broader fears that the Syrian war will trigger a revival of the long-standing hostilities between Israel and Hezbollah, which fought a fierce but inconclusive war in 2006 that killed 1,200 people. Many in Lebanon and Israel have long predicted a replay of Israel’s effort to vanquish the Shiite militia that threatens its northern border, and Hezbollah’s apparent efforts to boost its arsenal suggests that it is preparing for such an eventuality.

Israel’s chief worry is that a desperate Syrian regime might seek to ensure its survival by using Hezbollah to lash out with an attack against Israel, in fulfillment of Assad’s repeated warnings that his fall would generate regional chaos.

The main concern for the Shiite Hezbollah movement is that the collapse of the Syrian regime in Damascus and its replacement by one led by the overwhelmingly Sunni opposition will undermine its dominant role in Lebanon and leave it vulnerable to Israeli attack. The movement has long relied on Syria for the transshipment of arms supplied by its chief ally, Iran, and the fall of Assad would compromise its supply routes.

“Strategically, Hezbollah believes that Syria is the bridge for the resistance to bring in weapons,” Obeid said.

The State Department on Saturday condemned the latest example of sectarian violence, saying in a statement that it was “appalled” by the killings this past week in Baida, outside the town of Baniyas, in Assad’s native Latakia province.

Government forces and Alawite irregulars known as shabiha attacked the area with mortar fire, “then stormed the town and executed entire families,” the statement said.

It added, “We will not lose sight of the men, women and children whose lives are being so brutally cut short.”

On Saturday, hundreds of Sunnis fled the area around Baniyas after reports of another incident overnight Friday, in which at least eight deaths have been confirmed, according to the Britain-based Syrian Observatory for Human Rights. A video posted online showed the bloodied bodies of a man, several children and a baby with blackened legs.

Also Saturday, Assad made his second public appearance in three days, visiting Damascus University to inaugurate a statue dedicated to students who have died in the violence. Footage aired by state television showed him being mobbed by cheering, waving supporters.

Assad rarely appears in public, and his visibility this past week suggests his confidence has been buoyed by recent gains by his forces in some parts of the country and by indications that the international community remains reluctant to involve itself in the Syrian conflict, despite the reports that his regime has used chemical weapons.

Abigail Hauslohner and Ahmed Ramadan in Beirut, William Booth in Jerusalem and Anne Gearan, Greg Miller and Ernesto Londoño in Washington contributed to this report.