A US Army bus is towed away from the airport in Frankfurt March 2, 2011. A gunman shot dead two US soldiers at Frankfurt airport on Wednesday, regional authorities said, adding they were not ruling out a possible terrorist link. The gunman, who left two others seriously injured, was apparently a Kosovo national, said the Interior Minister for the state of Hesse, Boris Rhein.[Photo/Agencies]

FRANKFURT, Germany -- Two US airmen were killed and two others were wounded at Frankfurt airport Wednesday when a man opened fire on them at close range with a handgun, the first such attack on American forces in Germany in a quarter century.

President Barack Obama called the shooting an "outrageous act."

The alleged assailant, identified as a 21-year-old Kosovo man, was taken immediately into custody and was being questioned by authorities, said Frankfurt police spokesman Manfred Fuellhardt.

Family members in Kosovo described the suspect as a devout Muslim, who was born and raised in Germany and worked at the airport.

A bullet hole is seen in the window of the driver seat of a US Army bus outside the airport in Frankfurt March 2, 2011.[Photo/Agencies]

The attacker got into an argument with airmen outside their military bus before opening fire, killing the bus driver and one other serviceman, and wounding two others, one of whom was in life-threatening condition, Fuellhardt said. He said the attacker also briefly entered the bus.

The suspect then fled into the airport terminal, where he was quickly grabbed by two federal police officers and a US airman who had pursued him into the building, authorities said. He was disarmed without incident.

The victims, part of a group of about a dozen members of an Air Force military police and base security unit, had just arrived from England, the Air Force said.

They had landed at Frankfurt airport, one of Europe's busiest, and were waiting outside Terminal 2 to be driven to nearby Ramstein Air Base, which is often used as a logistical hub for operations in Afghanistan and Iraq. The two wounded airmen were taken to a hospital.

"I'm saddened and I'm outraged by this attack," Obama said at the White House. "I want everybody to understand that we will spare no effort in learning how this outrageous act took place."

In Berlin, German Chancellor Angela Merkel expressed sympathy for the victims and their families and pledged that Germany would do everything in its power to investigate the crime. "It is a terrible event," she said.

A tall blue barrier was erected around the bus as forensic experts examined it, and removed two bodies from the vehicle. As the bus was later towed away, a bullet hole was visible through the driver's side window.

The dead and wounded US airmen were not identified pending notification of their families. A Pentagon spokesman, Lt. Col. Todd Vician, said the airmen were on their way to an overseas deployment to Afghanistan, Iraq or elsewhere.