Brazil, Germany, Japan and India have launched a joint bid for permanent seats on the UN Security Council.
The four countries have pledged to back each other
"The Security Council must reflect the realities of the international community in the 21st Century," their joint statement said.
The four states pledged to back each other's case and said similar status should be given to an African nation.
The Council's five veto-wielding permanent members are Britain, China, France, Russia and the United States.
The 10 other Council members are chosen for two-year terms by regional groups.
UN Secretary General Kofi Annan is known to favour an expansion of the Council, to enable it to command greater respect - especially in the developing world - and to make it more effective.
The joint statement was issued after talks between Brazilian President Luiz Inacio Lula da Silva, German Foreign Minister Joschka Fischer, Japan's Prime Minister Junichiro Koizumi and Indian Prime Minister Manmohan Singh in New York.
The statement noted that there has been a nearly four-fold increase in the UN membership since it was founded after World War II in 1945, including a sharp increase in the number of developing countries.
"The Security Council, therefore, must be expanded in both the permanent and non-permanent categories, including
developing and developed countries as new permanent members," the joint statement said.
"It must be representative, legitimate and effective."
In a speech to the UN General Assembly, the Brazilian leader, known as Lula, said the Council's composition must reflect today's reality, rather than perpetuate the post-WWII era.
In another speech, Mr Koizumi said Japan's reconstruction role in Iraq and Afghanistan, and its efforts to resolve the North Korean nuclear issue, entitled it to a permanent seat on the Council.
Japan pays more money into the UN coffers than any nation except the US. Germany is the third-biggest contributor.
ELECTED MEMBERS FOR 2004
Algeria - until end of 2005
Angola - until end of 2004
Benin - until end of 2005
Brazil - until end of 2005
Chile - until end of 2004
Germany - until end of 2004
Pakistan - until end of 2004
Philippines - until end of 2005
Romania - until end of 2005
Spain - until end of 2004
Supporters of India's membership point out that the country is the world-largest democracy where some 1.2 billion people live, while some of Brazil's backers say it can make a strong case to represent South America.
"All four states regard themselves as natural candidates," Mr Fischer said after the talks.
The joint statement also said Africa must also have a permanent seat, amid reports that African leaders are currently discussing which of their states should be put forward.
However, historic regional animosities are likely to complicate the joint bid, analysts say.