AT THE BARRICADE:  A Free Syrian Army fighter peers out at a Syrian  army position during heavy fighting in Damascus. Picture: REUTERS
AT THE BARRICADE: A Free Syrian Army fighter peers out at a Syrian army position during heavy fighting in Damascus. Picture: REUTERS

SYRIA warned on Thursday of a possible "surprise" response to an unconfirmed attack by Israel on Syrian territory, while Lebanese Hezbollah Shiite militia, Russia and Iran offered support for President Bashar al-Assad.

Diplomats, Syrian rebels and regional security sources said on Wednesday Israeli jets had bombed a convoy near the Lebanese border, apparently hitting weapons destined for Hezbollah. But Syria denied this was the target, saying it was a military research centre northwest of Damascus.

Damascus may take "a surprise decision to respond to the aggression of the Israeli warplanes", Syria’s ambassador to Lebanon, Ali Abdul-Karim Ali, said. "Syria is engaged in defending its sovereignty and its land," he told militant group Hezbollah.

Syria and Israel have fought several wars and in 2007 Israeli jets bombed a suspected nuclear site, without a military response.

Iran-backed Hezbollah denounced the attack and urged widespread condemnation of the "barbaric aggression".

Senior Iranian officials arrived in Syria on Wednesday for a three-way meeting with Hezbollah, the pro-government Syria Steps website said.

Israel has remained silent on the attack and there has been little reaction from its western backers. Russia, which has blocked western efforts to put pressure on Syria at the United Nations (UN), said any Israeli air strike would amount to unacceptable military interference. "If this information is confirmed, then we are dealing with unprovoked attacks on targets on the territory of a sovereign country, which blatantly violates the UN charter and is unacceptable, no matter the motives to justify it," the foreign ministry said.

Iranian Deputy Foreign Minister Hossein Amir Abdollahian said the attack "demonstrates the shared goals of terrorists and the Zionist regime". Mr Assad portrays the rebels fighting him as foreign-backed, Islamist terrorists with the same agenda as Israel.

An aide to Iran’s Supreme Leader Ayatollah Ali Khamenei said on Saturday that Iran would consider any attack on Syria as an attack on itself, however Mr Abdollahian made no mention of retaliation on Thursday.

Hezbollah said the attack showed that the conflict in Syria was part of a scheme "to destroy Syria and its army and foil its pivotal role in the resistance front (against Israel)".

Details of Wednesday’s strike are sketchy and, in parts, contradictory. Syria said Israeli fighter jets, flying low to avoid radar, crossed into its airspace from Lebanon and struck the Jamraya military research centre. But diplomats and rebels said the jets hit a weapons convoy heading from Syria to Lebanon, apparently destined for Mr Assad’s ally, Hezbollah, and the rebels said they — not Israel — hit Jamraya with mortars.