Two US airmen from RAF Lakenheath have been killed and two more wounded in a gun attack on a bus at Frankfurt airport

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.

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.

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. He has now been taken into custody.

This morning Colonel John Quintas, 48th Fighter Wing commander, issued a statement about the shooting.

He said: 'It is with a heavy heart that I confirm that airmen from this wing were involved in a shooting incident at Frankfurt Airport.

'I would like to express my sincere appreciation for the outpouring of support from concerned citizens around the world including that of our commander in chief and our German partners.

'I would like to add my personal sympathy to the families and friends of the airmen that were killed or injured in the tragedy.

'You are in our thoughts and prayers. As you deal with this tragedy, you're not alone. We are your family.'

Meanwhile, US President Barack Obama promised to 'spare no effort' in investigating the killings.

The bus was transporting a Security Forces team assigned to RAF Lakenheath from the airport to the US Air Force's Ramstein base. They were on their way to support overseas military operations.

RAF Lakenheath in Suffolk 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.

'It is a terrible event,' she said.

The German news agency DAPD quoted Mr Rhein, the security minister who rushed to the scene of the shooting, as saying there were no indications of a terrorist attack.

However, a member of the US House homeland security committee, Patrick Meehan, said in Washington that it looked like a terrorist attack. He said he did not have all the facts yet and was still being briefed.

At Frankfurt airport, taxi cab driver Salimi Seraidon was sitting at a stand about 200 yards away when the attack took place and said it was over quickly as police rushed to the scene.

'We just heard the shots,' he said.

Kosovo interior minister Bajram Rexhepi identified the suspect as Arif Uka, a Kosovo citizen from the northern town of Mitrovica.

'This is a devastating and a tragic event,' Mr Rexhepi said. 'We are trying to find out whether this was something that was organised or what was the nature of the attack.'

The bus was transporting a security forces team assigned to RAF Lakenheath from the airport to the US Air Force's Ramstein base. They were on their way to support overseas military operations.

Mitrovica is best known for the ongoing ethnic division between majority ethnic Albanians and minority Serbs. The former mining town, however, has also been the focus of reports that it breeds radical Islamic extremists.