Israel launched an airstrike in the Syrian capital Damascus today.
It targeted a shipment of Iranian-made guided missiles believed to be on their way to Lebanon's Hezbollah militant group, an intelligence official in the Middle East claimed.
The attack, the second in three days, signalled a sharp escalation of Israel's involvement in Syria's bloody civil war.
The confirmation came hours after Syria's state media reported that Israeli missiles struck a research centre near the Syrian capital, setting off explosions and causing casualties.
The official told the Associated Press that, as with Friday's strike, the target was Fatah 110 missiles, which have very precise guidance systems with better aim than anything Hezbollah has in its arsenal.
Israel has said it will not allow sophisticated weapons to flow from Syria to the Lebanese Hezbollah militia, an ally of Syrian president Bashar Assad and a heavily armed foe of the Jewish state.
An airstrike in January also targeted weapons apparently bound for Hezbollah, Israeli and US officials have said.
The Syrian state news agency SANA reported early today that explosions went off at the Jamraya research centre near Damascus, causing casualties.
"Initial reports point to these explosions being a result of Israeli missiles that targeted the research centre in Jamraya," SANA said.
A Syrian activist group, the Britain-based Syrian Observatory for Human Rights, also reported large explosions in the area of Jamraya, a military and scientific research facility north west of Damascus, about 10 miles from the Lebanese border.
An amateur video said to be shot early today in the Damascus area showed a huge ball of fire lighting up the night sky.
Israel's first airstrike in Syria, in January, also struck Jamraya.
At the time, a US official said Israel targeted trucks next to the research centre that carried SA-17 anti-aircraft missiles.
The strikes hit both the trucks and the research facility, the official said.
The Syrian military did not confirm a hit on a weapons shipment at the time, saying only that Israeli warplanes bombed the research centre.
Israeli lawmaker Shaul Mofaz, a former defence minister and a former chief of staff, declined to confirm the airstrike but said Israel is concerned about weapons falling into the hands of the Islamic militant group amid the chaos of Syria's civil war.
"We must remember that the Syrian system is falling apart and Iran and Hezbollah are involved up to their necks in Syria helping Bashar Assad," he told Israel Radio.
"There are dangers of weapons trickling to the Hezbollah and chemical weapons trickling to irresponsible groups like al-Qaida."