WASHINGTON (AFP) - A coalition air strike in Syria has killed a senior Islamic State in Iraq nd Syria (ISIS) operative considered the group's information minister, a week after another raid eliminated a top ISIS strategist, the Pentagon said on Friday (Sept 16).

Pentagon spokesman Peter Cook said that Wa'il Adil Hasan Salman al-Fayad, also known as "Dr. Wa'il", was killed in a precision strike on Sept 7 near Raqa, the Syrian city that is the de facto capital of the ISIS extremist group.

"Wa'il oversaw ISIL's production of terrorist propaganda videos showing torture and executions," Cook said, describing him as "one of ISIL's most senior leaders" and a close associate of Abu Mohamed al-Adnani, the ISIS group spokesman killed on Aug 30.

ISIL is an alternative acronym for ISIS.

US officials "will continue to work with our coalition partners to build momentum" in the campaign to deal the ISIS group "a lasting defeat," he added.

ISIS is also referred to as Daesh.

The announcement comes as air strikes and clashes are testing a fragile ceasefire in Syria.

Under the deal, Moscow must pressure Syrian President Bashar al-Assad and Washington must work with Syrian rebels to silence their guns.

If the truce, which began on Monday, lasts seven days and humanitarian access is granted, Russia and the United States are to work together to target extremists, including ISIS and former Al-Qaeda affiliate Fateh al-Sham Front.

Russia said that although only Moscow and the Syrian regime were fulfilling the truce deal, it was ready to extend the agreement by 72 hours.

The Pentagon also said that it had deployed dozens of US Special Operations Forces to Syria's border with Turkey to fight ISIS at Ankara's request in support of the Turkish military and "vetted" Syrian rebels.