By Josh Smith

KABUL (Reuters) - American soldiers helping Afghan troops fight Islamic State in Afghanistan were forced to abandon equipment and weapons when their position came under fire, a U.S. military official said on Tuesday.

Islamic State fighters have circulated photographs of a rocket launcher, grenades, ammunition, identification cards, an encrypted radio and other equipment that they said they had seized.

U.S. military spokesman General Charles Cleveland said the loss had happened during fighting in Nangarhar, a province in eastern Afghanistan, in July in which at least five special forces soldiers were wounded, but he denied that any American positions were overrun.

"We have been able to determine that the I.D. card and most of the pictured equipment was lost during recent operations in southern Nangarhar," he said in a statement.

Cleveland said a location set up to deal with casualties - a routine step in any operation - had come under "effective enemy fire" and the soldiers moved to a safer position.

"In the course of moving the (casualty collection point) to a safe location, some equipment was left behind," he said. 

Despite the sensitive nature of some of the items, Cleveland said he did not expect there would be "any measurable operational impact" from the loss.

"For understandable reasons, the lives of soldiers were not put at risk to recover the equipment," he said.

At the time, military officials said five soldiers were wounded by small arms fire and shrapnel during fighting that spanned July 24 and 25.

Two of the wounded returned to duty and the three others were expected to make a full recovery, Army General John Nicholson said in July.

U.S. troops and aircraft have been taking a more active role against Islamic State after President Barack Obama authorized more military support for the Afghan government.

(Editing by Robert Birsel and Robin Pomeroy)