None of the victims have yet been publicly identified, pending notification of next of kin [Reuters]

German authorities have said they suspect an "Islamist motivation" over an attack by a German national of Kosovan descent arrested over the fatal shooting of two US airmen at Frankfurt airport. 

"In view of the circumstances, there is a suspicion that this was an act with Islamist motivation," said federal prosecutors after Wednesday's shooting on a bus at the airport.

The prosecutors have taken over the investigation into the shooting, which also injured two other US servicemen, one of them critically, and are working together with US authorities.

Officials say they do not think the man, a 21 year old who worked at the airport,  was part of a wider cell.

Boris Rhein, interior minister of the state of Hesse, said: "There are hints that he is a radicalised Muslim. The evidence to date indicates that he acted on his own.

"So far there is no network in the sense of a network visible for us. It is true that he was active on Facebook, that he was active in the frame of this network, but there is no network in the sense of, for instance, a terror cell."

The man was taken into custody immediately after the shooting and arrived at a federal court in Karlsruhe under heavy guard on Thursday.

The AP news agency reported that a top German security official had said that the man had confessed to the shootings.

'Substantial evidence'

Juergen Linker, a Frankfurt police spokesman, told the DAPD news agency that one serviceman remained in critical condition after being shot in the head. The other wounded airman was not in life-threatening condition, Linker said.

None of the victims have yet been publicly identified, pending notification of next of kin.

The alleged attacker's family in northern Kosovo identified him as Arid Uka, from the northern town of Mitrovica, whose family has been living in Germany for 40 years. 

In Mitrovica, relatives said the suspect was born and educated in Germany, and described the suspect as a devout Muslim who worked at the airport.

The German Spiegel newspaper's online edition said it had learned from German security sources and US authorities that there was "substantial evidence" that the attacker had links to "Islamist circles" in Germany.

The airmen killed in Wednesday's attack were on their way to overseas deployment via Germany [Reuters]

Angela Merkel, Germany's chancellor, condemned the shooting as a "terrible incident" and pledged a full investigation, while Barack Obama, the US president, called the attack an "outrageous act".

The victims, part of a group of about a dozen members of an air force military police and base security unit, had just arrived from England, the air force said.

They were waiting outside Terminal 2 of the airport, one of Europe's busiest, to be driven to nearby Ramstein Air Base, which is often used as a logistical hub for operations in Afghanistan and Iraq.

Todd Vician, a Pentagon spokesman, said the airmen were on their way to an overseas deployment to Afghanistan, Iraq or elsewhere.

The US embassy in Pristina, Kosovo's capital, said in a statement on Thursday that "the act of a single individual will in no way affect the deep and abiding friendship between our two countries".