Iran said it would review an offer of talks on its nuclear program with the United States and five other world powers, even as it prepared to declare new progress in its disputed atom activity on Thursday.

The United States, Russia, China, France, Germany and Britain said on Wednesday they would ask European Union foreign policy chief Javier Solana to invite Tehran to a meeting to find "a diplomatic solution to this critical issue."

"We will review it and then decide about it," Ali Akbar Javanfekr, a senior adviser to Iranian President Mahmoud Ahmadinejad, told Reuters.

Underlining Tehran''s determination to press ahead with its nuclear program, Ahmadinejad was expected to announce later on Thursday in the central city of Isfahan that Iran has mastered the final stage of atom fuel production.

The West suspects Iran is seeking to develop nuclear bombs. The Islamic Republic, which marks its National Nuclear Day, says it only aims to produce electricity.

The new U.S. administration of President Barack Obama is trying to reach out to Iran, offering a "new beginning" of diplomatic engagement after three decades of mutual mistrust.

Wednesday''s invitation to direct talks marked a major policy change in Washington, which under former President George W. Bush spearheaded a drive to isolate Iran over its nuclear work.

"We strongly urge Iran to take advantage of this opportunity to engage seriously with all of us in a spirit of mutual respect," the six powers said in a statement after a meeting of senior diplomats in London on Wednesday.