While praising a small group of European countries -- including Britain and France -- for boosting armed firepower, he said the majority were either leaving defence budgets unchanged or spending less in real terms on military resources.

"At a time when the need for our military forces is growing this is a disturbing trend," said Nicholas Burns, in a speech to a Brussels think tank, the European Policy Centre.

He pointed out that while the United States spends over 420 billion dollars on national defence, the combined defence budgets of the other 25 NATO allies was less than half that.

"That capabilities gap is worrisome," he said, in particular at time when the North Atlantic Treaty Organization (NATO) has expanded well beyond its Cold War-era European theatre of operations.

The United States is also pushing for NATO to expand its missions in Afghanistan and Iraq, while maintaining significant forces in the Balkans and boosting its ties in central Asia and the Middle East.

"If we are going to be in Afghaninistan, Iraq, Kovoso, Bosnia, if were going to have an outreach to the Middle East, the Caucasus, Central Asia, you need forces, well-equipped, well-trained forces," he said.

Other countries which have either boosted defence spending or reformed their armed forces to make military resources more useful include Poland, Denmark, the Czech Republic and Norway, he said.

The key problem was that European forces were less deployable than their US counterparts, he said, citing estimates that 75 percent of the United States 2.4 million-strong army could be rushed overseas, while only 3-5 percent of Europe's could, even if it has similar numbers of soldiers.

"They're not trained sufficiently or equipped or funded," he said. "This is our biggest problem in NATO. We have an inability generating a large number of forces," he said.

"At some point ... the rubber needs to meet the road. At some point you have to have the capabilities to back up your political ambitions and your rhetoric. And this growing disparity in capabilities worries us greatly."

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