JERUSALEM — Israeli warplanes carried out a strike deep inside Syrian territory on Wednesday, US officials reported, saying they believed the target was a convoy carrying sophisticated antiaircraft weaponry on the outskirts of Damascus that was intended for the Hezbollah Shi’ite militia in Lebanon.
The predawn strike was the first time in more than five years that Israel’s air force had attacked a target in Syria. While there was no expectation that the beleaguered Assad government had an interest in retaliating, the strike raised concerns that the Syrian civil war had continued to spread beyond its borders.
The US officials, who spoke on the condition of anonymity, said Israel had notified the United States about the attack, which the Syrian government condemned as an act of ‘‘arrogance and aggression.’’ Israel’s move demonstrated Tel Aviv’s determination to ensure that Hezbollah — its arch foe in the north — is unable to take advantage of the chaos in Syria to bolster its arsenal significantly.
In a statement, the Syrian military denied that a convoy had been struck. It said the attack had hit a scientific research facility in the Damascus suburbs that was used to improve Syria’s defenses and called the attack a flagrant breach of Syrian sovereignty and airspace.
Israeli officials would not confirm the airstrike. But the attack came after days of intense security consultations with Prime Minister Benjamin Netanyahu regarding the possible movement of chemical and other weapons around Syria, and warnings that Israel would take action to thwart any possible transfers to Hezbollah.
Thousands of Israelis have crowded gas-mask distribution centers over the last two days. On Sunday, Israel deployed its Iron Dome missile defense system in the north, near Haifa, which was heavily bombed during the 2006 war with Lebanon.
Syria and Israel are technically in a state of war but have long maintained an uneasy peace along their decades-old armistice line. Israel has watched warily and tried to stay out of Syria’s civil war, fearful of provoking a wider confrontation with Iran and Hezbollah. In November, however, after several mortars fell on Israel’s side of the border, its tanks struck a Syrian artillery unit.
Several analysts said that despite the increased tensions, the likelihood of retaliation for the airstrike was relatively low.
‘‘It is necessary and correct to prepare for deterioration — that scenario exists,’’ Danny Yatom, a former chief of the Mossad, Israel’s intelligence agency, told Ynet, a news website. ‘‘But in my assessment, there will not be a reaction, because neither Hezbollah nor the Syrians have an interest in retaliating.’’
In the United States, the State Department and Defense Department would not comment on reports of the strike.
The episode illustrated how the escalating violence in Syria, which has already killed more than 60,000 people, is drawing in neighboring states and threatening to destabilize the region further.
Iran has firmly allied itself with Syrian leader Bashir Assad, sending personnel from its Revolutionary Guards Quds Force to Syria and ferrying military equipment to Syria through Iraqi airspace.
Hezbollah, which plays a decisive role in Lebanese politics and has supported Assad throughout the uprising, has long relied on Syria as a source of weapons and a conduit for weapons from Iran. Some analysts think Hezbollah may be trying to stock up on weapons in case Assad falls and is replaced by a leadership that is hostile to the Shi’ite militia.
One US official said the trucks targeted Wednesday were believed to have been carrying sophisticated SA-17 anti-aircraft weapons. Hezbollah’s possession of such weapons would be a serious worry for the Israeli government, said Matthew Levitt, a former intelligence official who is at the Washington Institute for Near East Policy.
‘‘Israel is able to fly reconnaissance flights over Lebanon with impunity right now,’’ Levitt said. ‘‘This could cut into its ability to conduct aerial intelligence. The passing along of weapons to Hezbollah by the regime is a real concern.’’