Israel carried out a pre-dawn air strike near Damascus on Sunday, targeting Iranian missiles destined for Lebanon's Hezbollah in the second such raid on Syria in three days, a senior Israeli source said.
"The target was Iranian missiles which were destined for Hezbollah," he told AFP, speaking on condition of anonymity.
The attack targeted a facility just northwest of the Syrian capital, very close to the site of a similar attack late in January which was implicitly confirmed by Israel, the source said.
He also confirmed Israel was behind an earlier strike on a target very close to Damascus airport which took place early on Friday, which also struck Iranian arms destined for the Lebanese Shiite movement.
"Any time Israel learns about the transfer of weapons from Syria to Lebanon, it will attack," he warned.
According to Syria's official SANA news agency, Sunday morning's attack targeted the Jamraya military research centre near Damascus, in the Eastern Ghouta region.
Following the strike, the Israeli air force went on high alert, although the Jewish state was not anticipating a significant response from Damascus, the source said.
"The air force is now on high alert, the highest in recent years," he said.
On Sunday, an Israeli army spokeswoman said two batteries of the Iron Dome missile defence system had been moved to the north of the country.
And later in the day, the army ordered airspace in the north closed until May 9, resulting in the cancellation of flights from Haifa to Eilat, domestic carrier Arkia said in a statement.
Israeli media reported that security in embassies around the world was heightened due to the tensions.
Meanwhile, Prime Minister Benjamin Netanyahu left for a five-day visit to China after earlier postponing his departure to hold a security cabinet meeting to discuss the Syria developments.
Before take-off, Netanyahu refused to answer questions by reporters regarding the attack in Syria, and would only stress the importance of the visit to China.
The official Syrian news agency SANA accused Israel of being behind the attack as a show of support for the rebels fighting a two-year insurgency against the regime of President Bashar al-Assad.
"This new Israeli aggression is a clear attempt to alleviate the pressure on the armed terrorist groups after our army beat them back in several regions and after the army's victories on the road to recovering security and stability in Syria," said SANA.