He headed straight for informal talks with US President George Bush and United Nations Secretary-General Ban-Ki Moon, before meeting his fellow leaders.

Mr Brown and President Bush will lead calls for more of the 26 Nato members to commit fighting troops or extra resources to the battle against the Taliban.

The Prime Minister told reporters travelling with him: "What I want is the process of burden-sharing to be more effective over the next period of time."

Mr Brown will also seek clarification from French President Nicolas Sarkozy of his promise of 1,000 extra soldiers, provided certain conditions are met.

There may be more bitter wrangles with other alliance members who are still reluctant to share more of the military burden in Afghanistan, although Britain is keen to stress 40 countries already contribute in some way.

On Nato expansion, Mr Brown supports the plan to invite the Balkan states of Croatia, Albania and Macedonia to become full members and British officials expect that deal to go through - if only after last-minute wrangling.

But a row both within the alliance and with Russia is looming over former Soviet satellites Ukraine and Georgia bidding to take the first steps towards joining Nato with a formal Membership Applicant Plan.

President Bush is a staunch supporter of the states becoming members, but both France and Germany are against further expansion into what was once Russia's exclusive sphere of influence, and outgoing president, Vladimir Putin, is vehemently opposed to the move.

Mr Brown supports the two states' bid for MAP status but his spokesman said the UK would want to discuss the exact timing with allies.