BISHKEK, Kyrgyzstan —  A U.S. serviceman fatally shot a civilian at the U.S. air base in Kyrgyzstan on Wednesday "in response to a threat," the military said.

A statement released by the public affairs office at the Manas Air Base, where U.S. planes and military personnel are stationed, said an Air Force security forces serviceman "used deadly force in response to a threat at an entry control checkpoint."

The civilian was treated by Air Force medics and died at the base's emergency room, the statement from the 376th Air Expeditionary Wing said.

The Kyrgyz news agency Akipress said the man acted aggressive and tried to brandish a knife or similar weapon. The agency also cited unidentified Foreign Ministry officials as saying that U.S. Ambassador Marie L. Yovanovitch had delivered a note of regret to Kyrgyz officials and promised an investigation.

Base spokesman Maj. Don Traud declined further comment, saying investigators were still gathering information.

According to a senior military official in Washington, a driver of a fuel truck reportedly brandished a knife during a routine vehicle inspection. The driver was trying to gain access to the flight line at the base and was killed by an Air Force security airman who was acting in self-defense, the official said, speaking on condition of anonymity because the incident is still under investigation.

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Deputy Interior Minister Temirkan Subanov told The Associated Press that the man was shot twice at the base, located at the Manas airport just outside the capital, Bishkek.

Co-workers identified the slain man as Alexander Ivanov, a 42-year-old Russian who worked for a company called Aerocraft Petrol Management. Co-worker Sergei Pavlov said Ivanov had worked for four years for the company, which provides fuel services for Kyrgyz and international civilian aircraft, but not U.S. military aircraft.

Pavlov said the incident happened at an airport checkpoint controlled by U.S. military personnel. He said drivers traveling from a fuel depot to fill up aircraft must stop at the checkpoint and exit the truck while guards search the vehicle.

About 1,000 troops are located at the base, which the U.S. began using following the Sept. 11 terrorist attacks, primarily in support of military operations in nearby Afghanistan.

Kyrgyzstan and the United States have struggled this year to agree on terms for the continued leasing of the base, which took on greater importance last year after Uzbekistan evicted U.S. forces from a base there.

The Shanghai Cooperation Organization, a regional grouping that includes Kyrgyzstan, has called for the United States to set a timetable for closing bases in SCO countries.

The U.S. military makes refueling stops at an airport in Tajikistan's capital, but does not have a base there.

Russia did not object to the United States establishing the base in the wake of the Sept. 11, 2001, attacks, but officials in recent years have shown discomfort with an American military presence in an ex-Soviet republic.

Vladimir Zhirinovsky, a vehement nationalist who is vice-speaker of the Russian parliament, on Wednesday was quick to denounce the killing.

"The Americans conduct themselves like an imperial power and don't take responsibilities for their actions, and consider themselves the rulers of the entire planet," he said, according to the RIA-Novosti news agency.

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