Two US Air Force servicemen have been shot dead on a bus at Frankfurt airport in Germany. Two others have been seriously injured.
The shooting happened outside Terminal Two, near a US military bus, according to an airport police spokesperson.
German authorities say it is not clear whether the attack had a terrorist motive.
Police say a 21-year-old man from Kosovo has been arrested but his motives are unclear.
The airport is near the US military base at Ramstein which supports operations in Iraq and Afghanistan.
US President Barack Obama says the shootings are a stark reminder of the dangers faced by members of American armed forces around the world.