The US has attacked ISIS camps and militants in Syria, as Washington tries to prevent the militant group from rebuilding in the country after the fall of Bashar al-Assad's regime.

US Central Command said on Monday that 12 IS militants were killed in US airstrikes in areas controlled by the former Syrian regime and Russia.

"There is an ongoing US mission to disrupt, degrade and defeat ISIS that prevents the terrorist group from conducting external operations and ensures that ISIS does not find opportunities to regroup in central Syria," Centcom said.

General Michael Eric Kurilla said Washington and its regional partners will not allow ISIS to "take advantage of the current situation in Syria".