The problem has worsened in recent years as both NATO and the EU try to maintain rapid response forces.

The NATO Response Force (NRF) is supposed to be kept at a level of 25,000 soldiers. The EU, meanwhile, has 19 of its own 'battle groups' - groups of 1,500 soldiers that can be deployed to the world's hotspots at short notice.

But most EU member states are also NATO member state meaning that they make the same troops available for both organisations.

"We could only have a NRF that is not so strong," said the spokesman, with NATO currently debating what to do with the force which became fully operational last November but has not been on mission since.

NATO's problems have worsened in recent years with the US concentrating most of its military force in Iraq and the NATO mission in Afghanistan proving to be longer and more expensive than originally planned.

There are over 40,000 troops in Afghanistan and around 17,000 in Kosovo.

Over the last decade there has been simmering tension between the organisations as NATO tries to redefine itself after the Cold War and the EU has become more present on the world stage, and increasingly prepared to back its humanitarian and development goals up with peacekeeping forces.

"Soldiers that are active for the EU will be missed by us and vice versa," a NATO official told Der Standard.

"And in a crisis. To whom do the soldiers then really belong? The EU will lose out," the official added.