Two members of the US Air Force have been killed and two more wounded in a shooting at Frankfurt airport.
'Everything happened on board the bus,' police spokesman Juergen Linker told AFP news agency.
'The suspected gunman has been arrested. There are two dead and two seriously injured.'
Local authorities said the man attacked the bus, which was carrying service members about to fly home from Germany.
The interior minister for the state of Hesse, Boris Rhein, said the gunman was apparently a Kosovo national.
Security at the airport has been tightened and an investigation is under way.
German Chancellor Angela Merkel said: 'We don't know the details but I would like to express how upset I am. We have to do everything we can to find out what happened.'
US President Barack Obama has said he was outraged by the attack and the US would 'spare no effort' in learning how the attack took place.
