A man armed with a handgun has attacked a bus carrying US airmen outside Frankfurt airport, killing two Americans and wounding two others before being taken into custody, authorities said.
The airmen were based in Britain, at the RAF Lakenheath airfield in Suffolk.
Boris Rhein, the top security official in the German state of Hesse where the shooting took place, identified the gunman as a 21-year-old from Kosovo.
US President Barack Obama promised to "spare no effort" in investigating the killings.
The attack came as the bus sat outside the airport's Terminal 2, according to police. The bus driver and a passenger were killed, one person suffered serious wounds and another light injuries, he said.
The attacker and US military personnel apparently had an altercation in front of the bus just before the man started shooting, police said. The attacker also briefly entered the bus and was apprehended by police officers when he tried to escape.
US Air Force Europe spokeswoman Major Beverly Mock said all four victims were airmen. They were based in Britain, a US Air Force spokesman for the Lakenheath airfield said.
Lakenheath is home to the 48th Fighter Wing, the only F-15 fighter wing in Europe. It employs some 4,500 active-duty military members, as well as 2,000 British and US civilians.
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.
Kosovo interior minister Bajram Rexhepi identified the suspect as Arif Uka, a Kosovo citizen from the northern town of Mitrovica.
