|The airmen killed in Wednesday's attack were on their way to overseas deployment via Germany [Reuters]
An armed man has shot dead two US air force personnel in a bus parked outside Frankfurt airport in Germany.
The alleged assailant, identified as a 21-year-old Kosovan, was taken immediately into custody and was being questioned by authorities, Manfred Fuellhardt, the Frankfurt police spokesman, said.
He said the bus driver and one passenger were killed, while one person suffered life-threatening wounds and another light injuries in Wednesday's attack.
The German Spiegel newspaper's online edition said it had learned from German security sources and US authorities that there was "substantial evidence" that the attacker had links to "Islamist circles" in Germany.
The news site reported that several teams of investigators from the US were heading to Germany to research the background of the action and other possible dangers.
FBI agents were at the scene shortly after the shooting.
Boris Rhein, the senior security official in the German state of Hesse, had earlier told German media there were no indications of a terrorist attack.
Angela Merkel, Germany's chancellor, condemned the shooting as a "terrible incident" and pledged a full investigation, while Barack Obama, the US president, called the attack an "outrageous act."
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 were waiting outside Terminal 2 of the airport, one of Europe's busiest, to be driven to nearby Ramstein Air Base, which is often used as a logistical hub for operations in Afghanistan and Iraq.
Todd Vician, a Pentagon spokesman, said the airmen were on their way to an overseas deployment to Afghanistan, Iraq or elsewhere.
Nick Spicer, Al Jazeera's correspondent in Frankfurt, said there was currently no indication to the gunman's motive.
"We have to be careful before attributing any political significance to it all. It could be a person who is not mentally well who caused this.
"The fact that the fellows who were shot at came from a base that's far away suggests however there is not some personal motive - money, fighting over a woman, gambling, for instance."
Bajram Rexhepi, Kosovo's interior minister, said German police identified the suspect as Arif Uka, a Kosovo citizen from the northern town of Mitrovica.
In Mitrovica, relatives said the suspect's name was spelled "Arid" not "Arif," and that he was born and educated in Germany where his family moved some 40 years ago. They described the suspect as a devout Muslim, who worked at the airport.