Two U.S. 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.
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 U.S. 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.
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 U.S. 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.
Boris Rhein, the top security official in the German state of Hesse, told German media there were no indications of a terrorist attack.
Still, a member of the U.S. House Homeland Security Committee, Rep. Patrick Meehan, said in Washington that it looked like a terrorist attack. The chairman of the subcommittee that focuses on terrorism and intelligence added he did not have all the facts.
Kosovo Interior Minister Bajram Rexhepi identified the suspect as Arif Uka, a Kosovo citizen from the northern town of Mitrovica.
In Mitrovica, family members identified him as Arid Uka, saying that he was born and educated in Germany where his family moved some 40 years ago. However, German police said he was born in Kosovo.
An uncle, Rexhep Uka, said the suspect's grandfather was a religious leader at a mosque in a village near Mitrovica.
A cousin, Behxhet Uka, said he spoke to the suspect's father, Murat Uka, several times by telephone from Frankfurt after the family was contacted by Kosovo police. The father said all he knew was that his son did not come home from his job at the airport on Wednesday.
Behxet Uka said he would be shocked if Arid Uka was behind the shooting, saying that like the vast majority of Kosovo Albanians, the family is pro-American.
The northern town of Mitrovica is best known for the ethnic division between majority ethnic Albanians and minority Serbs. The former mining town has also been the focus of reports that it breeds Islamic extremists.
Western intelligence reports have said the region could be a recruitment ground for Muslims with Western features who could easily blend into European or U.S. cities and carry out terrorist attacks.
The Kosovo government said in a statement that it was "deeply moved" by what it branded as "a monstrous act" committed by a citizen of Kosovo origin.
"This macabre case is an individual act against the civilized values and the traditions of the Kosovo people who will always be thankful to the United States, the American people and the U.S. government for its strong backing of Kosovo," the statement said.
Kosovo remained part of Serbia amid the collapse of Yugoslavia in the early 1990s, but a struggle for independence by ethnic Albanians there eventually led to the Kosovo war in 1998. The bloodshed was halted in 1999 when NATO stepped in and bombed Serbia, followed by the deployment of peacekeepers. The NATO-led Kosovo Force still has 8,700 troops there provided by 32 nations, including the U.S. and Germany.
The last time American forces in Germany came under deadly attack was in the 1986 bombing of a disco frequented by U.S. servicemen. Two soldiers and one civilian were killed and 230 others were injured. A Berlin court later ruled the bombing was organized by Moammar Gadhafi's Libya.
A leftist terror group, the Red Army Faction, was also responsible for a string of attacks on Americans in the 1970s and 1980s before the group was disbanded in 1998.
More recently, German police thwarted a plot in 2007 to attack U.S. facilities by members of the extremist Islamic Jihad Union. Four men had planned to attack American soldiers and citizens at the Ramstein Air Base and other locations but were caught before they could carry out the plot.
The U.S. has drastically reduced its forces in Germany over the last decade, but still has some 50,000 troops stationed here.
The airmen shot in Frankfurt were stationed at the Lakenheath airfield in England, home to the 48th Fighter Wing, the only F-15 fighter wing in Europe.