US Secretary of State Hillary Clinton has raised concerns over the potential international impact of deep defence spending cuts in the UK, including to the Nato alliance.
Mrs Clinton took the unusual step of commenting publicly just days before the conclusions of a major defence review are announced in the UK.
On a visit to Brussels, she was asked by BBC Parliament if the cuts across Europe, and particularly in the UK, "worried" her.
"It does," she said. "And the reason it does is because I think we do have to have an alliance where there is a commitment to the common defence.
"Nato has been the most successful alliance for defensive purposes in the history of the world I guess, but it has to be maintained. Now each country has to be able to make its appropriate contributions."
Now each country has to be able to make its appropriate contributions. US Secretary of State Hillary Clinton.
On Monday, the results of the Strategic Defence and Security Review will be announced. The Treasury is looking for 10 per cent cuts to the Ministry of Defence's £37 billion budget. However, the MoD is arguing cuts should not be "draconian", and should instead be closer to 4 per cent in order to maintain the UK's military capabilities.
US Defence Secretary Robert Gates has also voiced similar concerns about defence cuts, but No 10 played down the comments from the US.
"Hillary Clinton was talking about defence cuts across Europe, and specifically in the context of Nato," a Downing Street spokeswoman said.
"She is absolutely right when she says that each country has to be able to make its appropriate contribution to common defence in Nato and Britain will always do that."
After talks with the Prime Minister on UK defence cuts, General Petraeus told a press conference he remained "confident" in the alliance between American and British troops.
"The UK has repeatedly been the partner on which we could repeatedly count.I'm quite confident that kind of relationship and reliance will still be founded in the future." General David Petraeus
"I have repeatedly received assurances that support for Afghanistan is iron clad," General Petraeus said.
He said "the UK has repeatedly been the partner on which we could repeatedly count.
"I'm quite confident that kind of relationship and reliance will still be founded in the future.
"In the six years of operational deployment alongside UK forces, particularly since September 11, [British] forces have performed magnificently. "
General David Petraeus described a matrix list he compiled of defence forces around the world and their abilities and willingness.
"Beyond the US there was only one other country with checks on all the boxes and that was the UK. I think that conveys my feelings," he said.
Britain must look at its "place in world" before defence cuts
The former head of the army, General Sir Mike Jackson, told Channel 4 News the Government needs to analyse Britain's place in the world before making big defence cuts.
He said: "I hope the defence review isn't simply a budget-cutting exercise, but stems from an objective and careful look at where Britain wants to be on the world stage."
Read more from General Sir Mike Jackson on defence cuts
Prime Minister David Cameron is believed to have had his last meeting with the MoD before the results of the review are announced.
There are expected to be job losses across the military, although military chiefs and Chancellor George Osborne have pledged these will focus on "backroom" staff. Equipment will also be cut, and there has been speculation that plans for a new aircraft carrier could be scrapped.
However, the UK's nuclear deterrent Trident will go ahead, Defence Secretary Dr Liam Fox pledged at the Conservative Party conference last week.
In an article in The Times today, he also vows that Britain will remain a "major contributor" to international alliances even after cuts.
Labour Shadow Defence Secretary Jim Murphy said no cuts should hit troops on the front line.
There must be no cuts to defence budgets that would hamper our support for British troops on the front line. Labour Shadow Defence Secretary, Jim Murphy.
"We must ensure that we maintain our military effectiveness so that our partnerships and alliances in Afghanistan remain strong," he said.
"There must be no cuts to defence budgets that would hamper our support for British troops on the front line. The Government must avoid rushing through enormous cuts that could permanently damage our ability to fulfil our military commitments."
Mrs Clinton's comments come as a National Audit Office (NAO) report shows that the "black hole" in the MoD equipment budget increased by £3.3 billion in the last 12 months of the Labour government.
The head of the NAO Amyas Morse said: "Central departmental decisions were taken to balance the defence budget which had the effect of driving very significant additional cost and delay into the equipment programme. This represents poor value for money for the taxpayer."
Dr Fox said the MoD had been "living beyond its means for too long" and his review would get spending under control.