Last week Rice told legislators in Washington the US was prepared to offer more military observers and police officers to future UN missions.

The announcement comes as a UN internal review revealed that peacekeeping operations were overstretched and needed clearer mandates from the Security Council, and more equipment and well-trained troops.

"That's extremely important and of course very different from the past ... very important for the whole peacekeeping operation"

Alain Le Roy, head of UN peacekeeping

The 15-member Security Council in a declaration to be adopted unanimously on Wednesday said peacekeeping mandates should be "clear, credible and achievable and matched by appropriate resources".

It also noted "the urgent need to increase the pool of available troop and police contributors".

The Better World Campaign, an advocacy group that focuses on US-UN relations, said the US' failure to pay its dues endangered UN missions in places like Sudan's western Darfur region, Haiti and the Democratic Republic of the Congo.

The US as the single biggest contributor is responsible for about 25 per cent of the world body's peacekeeping budget, which is about $8bn and pays for more than 110,000 soldiers and police in 15 separate missions worldwide.

Alain Le Roy, who heads the UN peacekeeping department, told reporters the US declaration was "extremely good news".

"That's extremely important and of course very different from the past," he said. "And of course that is very important for the whole peacekeeping operation."

Troubled relations

The previous US administration under George Bush had an uneasy relationship with the UN, often criticising it as inefficient and corrupt.

But Barack Obama, the US president, in pledging support for the UN and its peacekeeping operations asked the US Congress in June to settle all outstanding debts.

UN officials have privately criticised Western powers with strong militaries like Britain and the US for their unwillingness to provide troops to UN missions.

Britain and France are leading efforts to improve the efficiency and effectiveness of peacekeeping missions, some of which have faced charges of corruption and sexual abuse.