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

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 September 7 near Raqa, the Syrian city that is the de facto capital of the Islamic State jihadist 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 IS group spokesman killed on August 30.

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

The IS group is also referred to as ISIL and 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 jihadists, including the IS group 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 the IS group at Ankara's request in support of the Turkish military and "vetted" Syrian rebels.