TEHRAN: Iran has said it will strengthen Syria's air defences as part of a bilateral military deal aiming to "fight terrorism" and counter American pressure.

Key US ally Israel, Iran's arch-enemy, has launched hundreds of strikes in Syria since the start of a civil war there in 2011, including against Iranian forces.

Iran, one of President Bashar al-Assad's main allies in the conflict, has always denied sending forces to fight in Syria, saying it only has military advisors there.

Under the latest deal, "we will strengthen Syria's air defence systems in order to improve military cooperation between the two countries," Iranian state TV quoted armed forces chief Major General Mohammad Bagheri as saying.

The deal will "further enhance our will... to confront pressures by America," he added.

Along with Moscow, Tehran has played a key role supporting Assad in the war that has ravaged the country and killed more than 380,000 people, displacing millions.

Israeli strikes have meanwhile targeted government troops, allied Iranian forces and fighters from the Iran-backed Lebanese Shia militant group Hezbollah.

Syria was one of the few countries that helped Iran during the 1980-88 war with Iraq, and Tehran and Damascus signed a deal in 2006 sealing their military alliance. State TV's website on Wednesday published a video of Bagheri and Syria's Defence Minister Ali Ayoub signing the latest agreement in Damascus.