Israeli rockets have attacked a military research centre on the outskirts of the Syrian capital, Damascus, state television says.
The research centre hit on Sunday was also targeted by Israel in January, Reuters reports.
There was no immediate comment from Israeli officials on Sunday's explosions.
The BBC reported the Mount Qassioun area where large explosions were reported contains military installations that have been used to shell rebel-controlled areas.
On Saturday, Israel confirmed its warplanes had carried out a strike in Syria against a convoy of missiles heading for neighbouring Lebanon.
US President Barack Obama said Israel had the right to guard against the transfer of advanced weapons to Hezbollah.
President Bashar al-Assad is battling a two-year uprising which began with mainly peaceful protests that were met with force and grew into a bloody civil war in which the United Nations says at least 70,000 people have been killed.
Iran has condemned the attack on Syria and urged countries in the region to stand against the action.
Iran's Fars news agency paraphrased an Iranian Foreign Ministry spokesperson as saying Iran condemns the airstrike which it says is part of an effort by Israel to create instability and insecurity in the region.