Hillary Clinton said Nato members must make "appropriate" contributionsHillary Clinton says US worried over UK defence budget4 October 2010 Last updated at 17:17 ET
The US secretary of state told the BBC that Nato must be "maintained", as it was the "most successful" defensive alliance "in the history of the world".
Mrs Clinton's comments precede next week's defence spending review, when the scale of cuts will be revealed.
Downing Street said an agreement had been "very nearly" finalised.
The Treasury has been pushing for a reduction of up to 10% on the £37bn Ministry of Defence budget between 2011 and 2015.
However, leading military figures insist the UK's defensive capabilities must be maintained.
unhappycamper comment: Well Hillary, not every country is stupid enough to pour almost every discretionary $$$ into guns and war.