Syria has threatened to retaliate over what it says was an Israeli air raid, which threatens to take the conflict beyond Syria's borders, as Washington warned that Iran was stepping up support for Damascus.

Israel maintained a stony silence over Syria's claims, as well as over separate reports that its jets had hit a weapons convoy near the Lebanon border.

Syria's foreign ministry said Israel "and the states that protect it" are responsible for the air strike, and "affirms Syria's right to defend itself and its territory and sovereignty," state news agency SANA reported.

It called on "all the competent UN bodies to take the necessary steps given this grave Israeli violation, and to guarantee that it will not happen again."

UN chief Ban Ki-moon expressed "grave concern" and called on all parties to "prevent tensions or their escalation in the region."

Meanwhile US Secretary of State Hillary Clinton warned Thursday that Iran was stepping up its support for Syrian President Bashar al-Assad.AFP