By Michelle Nichols

UNITED NATIONS (Reuters) - Costa Rica nominated former United Nations climate chief Christiana Figueres on Thursday to be the next U.N. Secretary-General, making her the 12th candidate to enter the race ahead of the first Security Council secret ballot later this month.

"The United Nations, and the world, needs a Secretary-General who is a bridge builder, who can listen and consult, who can help resolve disputes, build agreements and anticipate problems. Christiana Figueres has proven to be that person," said Costa Rican President Luis Guillermo Solis.

Figueres recently ended her six-year tenure as executive secretary of the United Nations Framework Convention on Climate Change. She is credited by some diplomats for helping lead more than 190 countries to a global climate deal in Paris in December.

The search for a successor to Secretary-General Ban Ki-moon - a former South Korean foreign minister who steps down at the end of 2016 after two five-year terms - has sparked a push by more than a quarter of the 193 U.N. states for the organization's first female leader.

The other female candidates are: U.N. cultural organization UNESCO Director-General Irina Bokova of Bulgaria; former Croatian Foreign Minister Vesna Pusic; Moldova's former Foreign Minister Natalia Gherman; former New Zealand Prime Minister Helen Clark, who heads the U.N. Development Programme; and Argentine Foreign Minister Susana Malcorra, who was Ban's chief of staff until late last year.

Figueres told reporters her experience leading over 190 countries from the failed Copenhagen climate summit in 2009 to a global agreement in Paris in 2015 makes her qualified to lead the United Nations.

She said the success of the Paris climate agreement proves the U.N. is a relevant global body.

"Paris was one of the most successful negotiations of the United Nations," she said. "I believe I have proven my stripes."

But she added she would have a tough learning curve on broader issues of peace and security.

Also in the race are former Macedonian Foreign Minister Srgjan Kerim; Montenegro Foreign Minister Igor Luksic; former Slovenian President Danilo Turk; former U.N. High Commissioner for Refugees Antonio Guterres, who is also a former Portuguese prime minister; former Serbian Foreign Minister Vuk Jeremic; and Slovak Foreign Minister Miroslav Lajcak.

The 15-member Security Council will hold its first informal secret ballot on July 21 and hopes to agree on a candidate by September or October to formally recommend to the General Assembly for election.

Ultimately the council's veto powers - the United States, Britain, France, Russia and China - have to agree on a candidate. There is no requirement for the five to pay attention to the popularity of candidates with the General Assembly.

Under an informal tradition of rotating the top post between regions, it is Eastern Europe's turn and eight of the current nominees are from there.

At least two-thirds of the candidates are set to take part in two debates in the U.N. General Assembly on July 12 which will be broadcast live on al Jazeera.

(Additional reporting by Valerie Volcovici in Washington and Enrique Andrés Pretel in San Jose; Editing by Matthew Lewis and Chizu Nomiyama)