A U.S. military helicopter carrying six Marines and two Nepalese Army soldiers went missing during a mission in Nepal delivering aid to earthquake victims, U.S. defense officials said Tuesday, but so far there have been no indications that the aircraft crashed.

U.S. Army Col. Steve Warren said an Indian helicopter in the air nearby at the time heard radio chatter from the Marine aircraft about a possible fuel problem. He said the Huey, carrying tarps and rice, had dropped off supplies in one location and was en route to a second site when contact was lost. He said officials are hopeful that the aircraft is simply missing because there has been no smoke or other signs of a crash.

Navy Capt. Chris Sims says the Huey was conducting disaster relief operations near Charikot, Nepal, on Tuesday, around 9 a.m. EDT.

Warren said a Nepalese air brigade unit had seen the Huey, so Marines in V-22 Osprey aircraft searched near that last known location for about 90 minute but found nothing. Because it's now dark, members of the Nepalese Army are conducting the search on foot. Warren said they are moving toward the second aid location to see if the helicopter landed near there.

Because of the rugged mountainous terrain, the helicopter could have landed in a low area but the Marines may not be able to get a beacon or radio signal out, Warren said. He added that U.S. airborne para-rescue forces have rehearsed rescue missions, and are ready to go if needed.

The aircraft is part of Marine Light Attack Helicopter Squadron 469, and the incident is under investigation.

There are about 300 U.S. troops in Nepal assisting with the rescue mission, using a variety of aircraft including three Hueys, four Ospreys and several cargo planes.