Beijing will work with the United States to block a plan to add new permanent members to the UN Security Council, China's UN ambassador says.
Any successful bid to change the Council needs two-thirds majority
Wang Guangya said he agreed the deal with the new US ambassador to the UN, John Bolton, at a meeting.
Both countries oppose a plan put forward by the Group of Four - Brazil, Germany, Japan and India - to add six new permanent members to the Council.
Meanwhile, the African Union has voted to demand two veto-wielding seats.
The G4 had asked them to drop the veto demand.
Beijing does not want Japan to have a permanent seat on the Council and would prefer to see more developing countries.
China and the US have different reasons for opposing the G4 plan, says the BBC's Susannah Price at the United Nations in New York.
Washington supports Japan's bid, but only wants "two or so" new permanent members.
Mr Wang admitted that they would be working in parallel rather than together in the coming weeks, "because we have different friends in different parts of the world".
But he stated: "At this stage, I think 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.
"We agreed to work together to make sure that our interests are maintained."
It came as member countries of the African Union (AU) met in Ethiopia's capital, Addis Ababa, for an extraordinary summit.
There are deep divisions within the continent on which countries would take the two permanent seats offered to Africa under the G4 proposals.
Egypt, Nigeria and South Africa are the leading candidates but other states are far from happy about being relegated to the second division, says the BBC's Martin Plaut.
But the AU agreed it would stick to its demands for the Council to be enlarged from 15 to 26 seats.
They want six new permanent seats with veto powers - two of those for Africa - and five new non-permanent seats, of which two would also be for Africa.
The G4 has proposed a 25-member council, with six new permanent seats without a veto - four for them, and two for Africa - as well as four non-permanent seats.
UN members have been discussing the expansion of the Security Council for years, to reflect today's world rather than the balance of power following World War II.
UN Secretary General Kofi Annan has said he would like a decision on Council expansion before the UN summit of world leaders in September.