US says it has killed ISIS leader Abu Yusif in Syria

Washington has stepped up military action against the jihadist group since the fall of Bashar al-Assad's government earlier this month, hitting areas that were shielded by Syrian and Russian air defenses before a lightning offensive by rebels who now control the country.

The strike took place Thursday in Deir Ezzor province in eastern Syria, killing IS leader "Abu Yusif" and another operative, the US Central Command (CENTCOM) said on social media, without providing further details on the two jihadists.

"This airstrike is part of CENTCOM's ongoing commitment, along with partners in the region, to disrupt and degrade efforts by terrorists to plan, organize, and conduct attacks," CENTCOM said.

The strike "was conducted in an area formerly controlled by the Syrian regime and Russians," it added.

The United States has for years carried out periodic strikes and raids to help prevent a resurgence of IS, but has launched dozens of strikes since Assad's fall.

On December 8 -- the day rebels took the capital Damascus -- Washington announced strikes on more than 75 IS targets that CENTCOM said were aimed at ensuring it "does not seek to take advantage of the current situation to reconstitute in central Syria."

And on Monday, CENTCOM said US forces killed 12 militants from the group in strikes it said were carried out "in former regime and Russian-controlled areas."