CHALDOVAR, Kyrgyzstan (AP) — An American military refueling plane carrying three crew members crashed Friday in the rugged mountains of Kyrgyzstan, the Central Asian nation where the U.S. operates an air base key to the war in Afghanistan.

There was no word on the fate of the KC-135 crew as darkness fell and the search for them was suspended for the night. Cargo planes do not have ejector seats. Officials at the U.S. base said they had no information yet on the cause of the crash.

The plane crashed at 2:55 p.m. near Chaldovar, a village 100 miles (160 kilometers) west of the U.S. Transit Center at Manas base outside the Kyrgyz capital, Bishkek. Pieces of the plane, including its tail, were scattered across in a grassy field bordered by mountains; the air was infused with the heavy stench of fuel.

The plane was on a refueling mission for Afghanistan war operations at the time of the crash, a U.S. defense official in Washington said, speaking anonymously because he was not authorized to discuss the details of an ongoing investigation.

The front section of the aircraft has not yet been found, Kyrgyz Emergencies Minister Kubatbek Boronov told The Associated Press. He said searchers also have not found the flight recorders from the plane, which was badly burned in the crash.

The search for the crew will resume Saturday morning and the crash site will remain under guard, Boronov said.

One resident of the agricultural and sheep-grazing area said the plane exploded in flight.

"I was working with my father in the field, and I heard an explosion. When I looked up at the sky I saw the fire. When it was falling, the plane split into three pieces," Sherikbek Turusbekov told an AP reporter at the site.

The U.S. base, which is adjacent to Manas International Airport outside Bishkek, was established in late 2001 to support the international military campaign in Afghanistan. It functions as an interim point for troops going into or out of Afghanistan and as a home for the tanker planes that refuel warplanes in flight.

The Manas base has been the subject of a contentious dispute between the United States and its host nation.

In 2009, the U.S. reached an agreement with the Kyrgyz government to use it in return for $60 million a year. But the lease runs out in June 2014, and the U.S. wants to keep the base longer to aid in the withdrawal of troops from Afghanistan. Kyrgyzstan is reluctant to extend the lease.

On Monday, a Boeing 747 cargo plane crashed just after takeoff from the U.S. military base in Bagram, Afghanistan, killing all seven people aboard. The National Transportation Safety Board is investigating that crash since it was on the Bagram air base.

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AP writers Jim Heintz in Moscow and Robert Burns in Washington, D.C., contributed to this report.