Three Marines were killed and seven injured in an accident in Iraq on Tuesday while they were handling a rocket-propelled grenade launcher, U.S. Central Command said.

The Marines with the 1st Marine Expeditionary Force were firing the RPG — one of the more common weapons used by paramilitary, Fedayeen and other groups that have threatened U.S. and British forces — to familiarize themselves with it.

The launcher malfunctioned, U.S. officials said.

The accident occurred Tuesday evening in a remote area near the southern Iraqi city of Kut, officials said.

The names of the Marines were being withheld until their next of kin could be notified. The accident was under investigation.

Prior to these deaths, 128 U.S. troops have been killed in the war, the Pentagon said.