Beijing ambassador to the UN Wang Guangya said he reached the agreement with John Bolton during the US ambassador's first full day in his new post because both believe the proposal by the so-called Group of Four would divide the UN's 191 member states.

Washington and Beijing are on record as opposing the G4 resolution for different reasons, but the agreement would mark a new joint effort to prevent its approval by the UN General Assembly, which requires a two-thirds ``yes'' vote.

Wang said the ultimate objective of China and the US is to expand the Security Council with a formula that is not divisive. ``But at this stage, our objective will be to oppose the G4, to make sure they do not have sufficient votes to take the risk to divide the house.''

But he said Washington and Beijing will work in parallel in the coming weeks to block the resolution - not together - because ``we have different friends in different parts of the world.''

After 10 years of seemingly endless debate, Secretary-General Kofi Annan told UN member states in March that he wanted a decision on Security Council expansion before a summit of world leaders in September. But the issue remains highly contentious, and no proposal on the table at the moment can win the required two-thirds support.

The US-China effort to defeat the G4 was felt as an emergency summit of the African Union opened Thursday to consider whether to approve a compromise agreement that some of its ministers reached with Brazil, Germany, India and Japan in London July 25. The 53 African nations are known to be divided.

The Security Council now has 15 members, 10 elected for two-year terms and five permanent members - the US, Russia, China, Britain and France.

Brazil, Germany, India and Japan have introduced a resolution calling for a 25-member council that would add six permanent seats without a veto and four nonpermanent seats. They are hoping to win four of the permanent seats with the other two earmarked for Africa.

The African Union has proposed expanding the council to 26 members - adding six permanent seats with veto power and five non-permanent seats.

There is widespread support for enlarging the council to reflect the world today rather than the global power structure after World War II when the UN was formed. But all previous attempts have failed because of national and regional rivalries.