Former New Zealand Prime Minister Helen Clark has ended months of speculation by announcing her candidacy to become the next UN secretary-general.
In an interview with the BBC she said she would like the Security Council "to look more like the 21st Century".
She said Germany, Japan, India and Brazil would be "obvious candidates" to become permanent members.
She also referred to a proposal for two African states to become permanent members.
Ms Clark is the current head of the UN's Development Programme.
She argues that she has the right mix of proven experience to take over from Ban Ki-moon, who retires in December. She says the UN needs a new set of tools to face modern peace and security issues.
Three other women are vying to become the UN's first female secretary general. Four men are also candidates. There have so far been nine post holders, all men.
"The security council reflects the geo-political realities of 1945," Ms Clark told the BBC's Newsnight programme. "I would like it to reflect the 21st century world which we live in today."
Earlier the former prime minister told the AFP news agency that she was putting herself forward because of her proven leadership experience over nearly 30 years both in New Zealand and at the UN.
Other candidates for the secretary-general position include Unesco chief Irina Bokova of Bulgaria and the former High Commissioner for Refugees, Antonio Guterres, of Portugal.
New Zealand Prime Minister John Key recommended Ms Clark as the country's candidate at a press conference in Wellington on Monday.
"Having served as the prime minister of New Zealand for nine years and held one of the top jobs in the United Nations for the past seven, Helen Clark has the right mix of skills and experience for the job," he said.
Current UN Secretary General Ban Ki-moon was re-elected to serve a second five-year term, in a vote at the UN General Assembly in New York in 2011.