Israeli raids have hit three military sites outside Damascus, the second such reported attack in 48 hours, prompting a flurry of warnings from the international community.
The raids on Sunday reportedly targeted weapons bound for Lebanese group Hezbollah and raised new concerns that the conflict could spill over.
Israel deploys Iron Dome batteries to north
Are Mariah Carey and James Packer over?
Trump opens hotel blocks from White House
Iceland's Pirate party
Two earthquakes hit central Italy
Can Florida give Trump a path to White House?
Schoolchildren among the dead in Idlib attack
Calais 'Jungle' burns
Israel deploys Iron Dome batteries to north
Two 'Iron Dome' anti missile batteries were deployed in northern Israel on Sunday, local media reported.
Heavy explosions rocked the area around Mount Qassioun in the early hours of Sunday and amateur videos posted online show huge orange fireballs ballooning into the night sky after the attack, believed to have targeted the Jamraya Military Centre.
Syrian state television reported: ''The new Israeli attack is an attempt to raise the morale of the terrorist groups which have been reeling from strikes by our noble army.''
The international community scrambled to respond. UN Secretary General Ban Ki-moon expressed ‘‘grave concern’’, his spokesman Martin Nesirky said.
‘‘The secretary general calls on all sides to exercise maximum calm and restraint, and to act with a sense of responsibility to prevent an escalation of what is already a devastating and highly dangerous conflict,’’ Mr Nesirky said.
Egypt condemned the strikes as a ‘‘violation’’ of international law and the Cairo-based Arab League demanded UN Security Council intervention to stop such Israeli attacks.
Iran’s Defence Minister General Ahmad Vahidi said ‘‘the assault, which was carried out with the US green light, unveils the links between the terrorist mercenaries and their masters of the Zionist regime.’’
Britain warned of the ‘‘increasing danger to the peace of that entire region from the Syria crisis just getting worse and worse.’’
Turkish Prime Minister Recep Tayyip Erdogan, meanwhile, delivered his harshest attack yet against President Bashar al-Assad, calling him a ‘‘butcher’’ and warning that he will ‘‘receive his judgment in this world’’ for the deaths of thousands of Syrians.
‘‘If God permits, we will see this butcher, this murderer receive his judgement in this world... and we will praise (God) for it,’’ Erdogan said after the Israeli strikes.
As criticism mounts over US President Barack Obama's muted response to the Syrian crisis, key defence commentators inside Israel said its attempt to deter the transport of ''game-changing'' weapons from Syria to Lebanon risked failure.
Alex Fishman, defence commentator for the daily Yedioth Ahronoth, wrote: ''Preventing the convoy of weapons from leaving Syria for Hezbollah is beginning to look a lot like the ritual of the targeted killing operations in Gaza: real time intelligence, a swift closure of the circle of fire, destruction. Until the next convoy …
''That is going to force Israel into a Sisyphean ritual of staging attacks in Syria, which will go hand in hand with taking the risk that this conflict could spiral out of control, and that one of these operations could result in a regional conflagration.''
His concerns were echoed by Maariv's military affairs correspondent, Amir Rapaport, who warned it was ''by no means self-evident that the summer of 2013 will conclude without a war''.
The New York Times reported Israel's first attack, early on Friday, targeted a shipment of short-range, ground-to-air missiles that were bound for Hezbollah. Syria denied the attack had occurred.
In late January, an Israeli air strike targeted a suspected SA-17 anti-aircraft missile shipment intended for Hezbollah near the Jamraya centre. Both missile systems are viewed by Israel as potentially ''game-changing'' weapons that could significantly threaten Israel's security should they reach Hezbollah in Lebanon.
The missiles have a range of more than 200 kilometres and could bear chemical agents.
Jonathan Spyer, a senior research fellow at the Interdisciplinary Centre in Herzliya, warned that further attacks inside Syria could provoke a reaction from Hezbollah.
The attacks coincided with reports of a terrifying campaign of sectarian violence and massacres in the Syrian coastal town of Baniyas and the Sunni village of al-Bayda. There are fears that hundreds have been killed in the three-day assault by forces loyal to President Bashar al-Assad. Online videos show dozens of bodies, many shot in the head.
''After al-Bayda village massacre, where at least 51 civilians [were] slaughtered by knives or shot to death by Syrian Government's armed forces … we documented 160 civilians killed in Ras al-Nabaa district in Banias, including 26 children and 22 women, slaughtered and burned,'' the Syrian Network for Human Rights said. Hundreds of families have fled the area, opposition activists say.
Mr Obama would not comment on the reported strikes against Syria. ''I'll let the Israeli government confirm or deny whatever strikes that they've taken,'' he told a Spanish-language network.