LONDON -- The U.S. Army chief of staff says cuts in British defence spending may undermine the nation's ability to be an effective ally in future military operations.

Gen. Raymond Odierno questioned Britain's capability Monday in the Daily Telegraph, saying that the U.S. is reviewing the role of British troops in future conflicts as the U.K. considers reducing military spending to less than the 2 per cent of gross domestic product expected of NATO members.

"I would be lying to you if I did not say that I am very concerned about the GDP investment in the U.K.," he said.

Prime Minister David Cameron is under fire from members of his Conservative Party who want to protect defence spending from further cuts as the government struggles to balance the budget after the financial crisis. Some Conservatives want the party to commit to maintaining the 2 per cent level ahead of this year's election, but Treasury chief George Osborne has refused to do so.

Odierno suggested that Britain would no longer be able to contribute division-strength levels of 10,000 troops or more. That would suggest that British forces would have to operate within U.S. structures rather than beside them.

"In the past we would have a British Army division working alongside an American division." he is quoted as saying. "Now it might be a British brigade inside an American division, or even a British battalion inside an American brigade."

Former defence secretary Liam Fox said he'd find it "hard to swallow" if military spending falls while the government maintains its pledge to spend 0.7 per cent of GDP on the humanitarian aid budget.

A Royal United Services report, based on Ministry of Defence planning assumptions, predicted that spending will fall to 1.88 per cent of GDP in the next fiscal year, 1.71 per cent in 2020-21 and 1.57 per cent by 2025-26.