NEW YORK (Reuters) - Italian Prime Minister Romano Prodi said isolating Iran was a risky strategy and he was to meet President Mahmud Ahmadinejad later on Wednesday because it was vital to leave no stone unturned to resolve the nuclear crisis.

U.S. President George W. Bush and Ahmadinejad clashed over Iran's nuclear ambitions in separate speeches at the United Nations General Assembly on Tuesday and Washington is pressing its allies to consider imposing sanctions against Iran.

Prodi, who will be the first EU head of government to meet with Ahmadinejad, said all options were open, from negotiations to action at the UN Security Council to possible sanctions.

"It's amazing in such a serious situation to see that many of the main protagonists of the matter have never talked to each other," he said.

Foreign ministers of the major powers -- the United States, Russia, China, Britain, France and Germany -- agreed to give European Union foreign policy chief Javier Solana more time to explore a deal with Iranian negotiator Ali Larijani.

Prodi said Ahmadinejad had initiated the meeting scheduled for Wednesday afternoon, and he accepted the invitation in the hope of being able to influence him.

"I've seen that many people are surprised, but I'm convinced that we can't leave any effort undone to reach a solution," Prodi told reporters in New York. "I'm going into this meeting with no naivete, without thinking that it can in itself lead to a solution, but conscious of the risks that isolation of Iran can lead to," he said. "It will be a frank and sometimes hard conversation."

"We have to make a big effort to make sure conflicts don't break out without seeking solutions," Prodi said.

Solana has said he is making "real progress" in talks with Tehran and he is expected to meet Larijani soon.

A Spanish official said Ahmadinejad might stop over in Madrid on his way back to Iran but there were no plans for him to meet Prime Minister Jose Luis Rodriguez Zapatero.