UN Secretary General Kofi Annan has cut short a holiday to return to New York for last-minute talks aimed at securing a deal on reforming the world body.
UN Secretary General Kofi Annan has set out plans for wide reforms
UN member states are debating a draft document which the General Assembly had hoped would be adopted at next month's summit marking 60 years of the UN.
But last week, the US produced a series of objections to the document.
Critics now fear the UN could end up with a short statement of principles rather than one of substantive reforms.
Mr Annan had been on holiday in his home country of Ghana.
He is now due back at UN headquarters Wednesday morning, almost a week earlier than expected, says the BBC's Michael Voss in New York.
A group of about 30 countries has been given the task of reaching a consensus on a range of contentious issues before world leaders gather in New York in mid-September.
Mr Annan had hoped to use the summit to push through a series of reforms aimed at redefining the organisation for the 21st Century.
These include management changes as well as fresh action to meet its millennium goals to reduce poverty and promote development.
After six months of discussions, a 38-page draft document was presented to the General Assembly earlier this month.
Then, last week, the new US Ambassador to the UN, John Bolton, stepped in, asking for hundreds of changes.
The US objects to references to the International Criminal Court, action on global warming and increases in development aid.
At the same time it wants greater commitment to tackling terrorism and nuclear proliferation.
The UN has set itself a deadline of the end of this week to produce a new document.