Five US special forces troops have been wounded fighting the Islamic State group in eastern Afghanistan, General John Nicholson, the US commander said Thursday.

Two of the troops have returned to duty after being treated for their wounds, while the other three were expected to recover fully, General John Nicholson, who heads the NATO force in Afghanistan, said in a video conference from Kabul.

The Americans were wounded "in the last several days" while taking part in a joint operation with Afghan army troops in eastern Nangarhar province, Nicholson said.

The Afghan army has intensified operations against IS since the jihadists claimed two bombings over the weekend in Kabul that left 80 dead and 231 wounded.

Afghan's defense ministry has said the army is on the verge of dismantling IS in the eastern border region where it first appeared in 2014.

Nicholson said the IS fighters were "retreating south into the mountains of southern Nangarhar as we speak."

The group has an estimated 1,000 to 1,500 fighters in Afghanistan, down from about 3,000 in January, he said.

There are about 9,800 US troops in Afghanistan with a mission to advise and assist the Afghan military but also to fight extremist groups like Al-Qaeda or IS.

"We will continue to stay after Daesh until they are defeated here in Afghanistan," Nicholson, using an Arabic acronym for IS.