Israeli attacks on Iranian-supplied missiles in Syria acts of self-defense: Bolton 

US National Security Adviser John Bolton on Wednesday voiced support for Israeli strikes in recent months on sites in Syria where he said Iranian-supplied missiles and other "threatening weapons" had been deployed.

"I think that's a legitimate act of self-defence on the part of Israel," he said at a news conference in Jerusalem.

Russia, Syrian President Bashar al-Assad's big-power backer, says it is committed to destroying Islamic State insurgents but has been more circumspect about the involvement of Iran, another foreign power reinforcing Damascus.

The Idlib region, a refuge for civilians and rebels displaced from other areas of Syria as well as powerful jihadist forces, was hit by a wave of air strikes and shelling this month, in a possible prelude to a full-scale government offensive.

In April, the Trump administration mustered a coalition of US, French and British forces to attack Syrian government facilities related to the production of chemical weapons after a poison gas attack killed dozens of people in Douma district.

Bolton said that the US would respond "very strongly" if chemical weapons were used in Syria.

Damascus, endorsed by Moscow, has denied using the use of such weapons.