A gunman has shot dead two US military servicemen and injured two more in an attack on a bus outside terminal two at Frankfurt airport. It remains unclear what the motives of the gunman were but a Kosovan man was apprehended shortly afterwards. The bus was on its way from the airport to the Ramstein airbase.

Although the identities of the victims cannot be revealed until the next of kin have been notified, a spokeswoman for the US air force confirmed that all four were American airmen currently based at Lakenheath in the UK.

According to local police an argument appears to have broken out just before shots were fired. One of those who was killed appears to have been the bus driver and the other was a passenger whose body was discovered outside the vehicle. The identity of the accused has not been officially released but Bajram Rexhepi, Kosovo’s minister for the interior, said it was Arif Uka from Mitrovica.

Rexhepi added that the circumstances were tragic and that everything was being done to find out why the attack took place and whether it had been organised. US President Barack Obama said he was outraged and saddened by the news adding that the US would do all it can to find out what happened and why.

Jurgen Linker from the Frankfurt police said although the events appear to have taken place on the bus it was far too early to start guessing at a motive. The two injured men have reportedly suffered wounds to the head and chest.