Frankfurt - Two men died and two were wounded at Frankfurt airport on Wednesday when a Kosovo-born man opened fire inside a bus carrying US soldiers, apparently after some kind of dispute, German police said.
It was not clear at first if the gunman's motive was political or not. In Berlin, Chancellor Angela Merkel voiced shock but said she had received no details yet.
The 21-year-old assailant ran from the scene, but was overpowered and arrested by federal police in the nearby airport terminal.
He shot three US soldiers and the bus driver in the incident, police said. It appeared that the driver, who died slumped over the steering wheel, was also a US serviceman. Merkel described both dead as US soldiers.
Police admitted they were puzzled about how the violence broke out.
The US military was tight-lipped about the incident, but the government of neighbouring Rhineland Palatinate state said the bus had been about to depart for Ramstein Air Force Base in that state, the biggest US military airfield in Europe.
Boris Rhein, interior minister of Hesse state, where the attack occurred, said the suspect was 21, had roots in Kosovo and lived in the Frankfurt area.
At the scene, Rhein stressed that he was not using any words to suggest it was a terrorist attack and was calling the incident a homicide only, but added, 'At the moment, I don't rule anything out.'
Police spokesmen said the incident began inside the military bus. One soldier was found dead on the road in front of the bus. The wounded men were shot in the head and in the chest respectively.
The incident just before 3:20 pm local time (1420 GMT) occurred in a bus lane in a publicly accessible part of the airport outside Frankfurt Terminal 2. Police had no word on how many occupants had been in the bus.
The weapon was a pistol, possibly a revolver, police said.
Merkel said: 'Today there was an incident in which two American soldiers were killed at Frankfurt Airport.
'I want to express my shock and say that we will do all we can to investigate what happened. It is a dreadful incident and Germany will to all it can to bring clarity to this matter.'
Kurt Beck, premier of Rhineland Palatinate, said, 'We will be doing all in our power to protect US citizens in our state.'
US military buses regularly shuttle to the airport from US bases, picking up personnel coming in on commercial flights and dropping off servicemen and servicewomen heading home to the United States.
Operations at the huge airport continued uninterrupted after the incident. The airport is Germany's biggest, serving 119 airlines and processing 150,000 passengers every day. The crime scene was cordoned off as police gathered evidence.