Israeli warplanes struck weapons inside Syria that were bound for the Lebanese militant group Hezbollah, American and Israeli officials say.
The attack, which reportedly took place Friday morning, was the second such strike this year, further raising fears that Syria's two-year civil war could spill over into neighboring countries.
News of the strike comes as graphic evidence emerges of what a watchdog group says are scores of deaths in fighting and mass executions by forces loyal to President Bashar al-Assad in and around the coastal city of Baniyas.
Hundreds are reportedly fleeing amid fears of further sectarian-fueled violence.
Unidentified Israeli officials told The Associated Press that the targets of the strike were sophisticated "game-changing" weapons, including long range ground-to-ground missiles. It was unclear from the officials' reports where it took place and whether Israel's warplanes had attacked from Syrian or Lebanese airspace.
The Israeli Prime Minister's office and military declined to comment, which is the standard response following a secret operation. Israel has repeatedly warned that it would not hesitate to act to prevent its enemies from getting there hands on weapons, particularly chemical weapons.
The Reuters news agency reported that Prime Minister Benjamin Netanyahu secretly convened his security cabinet on Thursday night, ahead of the attack.
American officials first told news outlets on Friday night that the strike had taken place overnight Thursday, which was followed Saturday by the anonymous Israeli response.
Syrian state media made no mention of the strike and Syria's ambassador to the United Nations said he was not aware of any attack.
In January, Syrian officials responded quickly when Israeli warplanes are believed to have targeted a convoy carrying Russian-made SA-17 surface-to-air missiles, which were also said to be bound for Hezbollah.
There hasn't been an outright claim of responsibility by Israel, but days after that strike, then-Defense Minister Ehud Barak said: "That is another proof that when we say something we mean it. We say that we don't think it should be allowable to bring advanced weapons systems into Lebanon."
A top Israeli defense official dismissed the confirmation of the Friday strike, but not the strike itself.
"I don't know what or who confirmed what, who are these sources?" asked Amos Gilad, a senior strategist in the ministry. "In my book only the [military] spokesperson unit is official."
There is no suggestion that any of the weapons struck allegedly were chemical weapons and Gilad said he believes Hezbollah doesn't want them.
"Syria has large amounts of chemical weaponry and missiles. Everything there is under [regime] control," Gilad said, according to Israeli reports. "Hezbollah does not have chemical weaponry. We have ways of knowing.
"They are not keen to take weaponry like this, preferring systems that can cover all of the country [of Israel]," he added, referring to the estimated 60,000 rockets in Hezbollah's arsenal.
The State Department said today that is it "appalled" by reports of scores killed in the Sunni Muslim town of al Bayda, just south of Baniyas, by government forces and loyalist militiamen known as "shabiha" who largely belong to Assad's Alawite sect.
The Syrian Observatory for Human Rights watchdog group said at least 51 people, including women and children, were summarily executed on Thursday in al Bayda.
That was followed by reports of more deaths in the Ras-al-Nabaa neighborhood of Baniyas.
The SOHR said hundreds of Sunni families were fleeing south to the port city of Tartous to escape what they said was sectarian killing by the regime.
State television said there were operations in the area that "drove back several terrorist groups" and showed rows of weapons it said had been seized from rebels. Rebel groups led by extremist fighters had been mounting operations in that area.
Also on Saturday, Assad visited Damascus University to greet students and inaugurate a statue for student "martyrs" of the two-year conflict. A photo showed the Syrian president getting a warm reception from students reaching out their hands to greet him.
The display of confidence was his second public event this week: On May Day, he thanked workers at a Damascus power plant.