Mahmoud Ahmadinejad proposed on Monday a face-to-face debate with President Barack Obama at the United Nations if he is re-elected next month as Iran''s president.

But he balanced the offer with a sharp rebuke to Washington and its allies over Iran''s nuclear program. He reiterated that Iran would never abandon its advances in uranium enrichment in exchange for offers of easing sanctions or other economic incentives.

The nuclear issue "is closed," he told a news conference.

Obama has urged a "serious process of engagement" after Iran''s elections in an effort to end a nearly 30-year diplomatic chill. However last week, the American leader said the U.S. was prepared to seek deeper international sanctions against Tehran if it did not respond positively to the attempts to open negotiations on its nuclear program. Obama set a year-end deadline for Iran to show it wanted to engage with Washington.

The tough talk on nuclear negotiations following Iran''s test last week of a long-range missile appear aimed at burnishing Ahmadinejad''s hard-line credentials in the election campaign against another conservative and two pro-reform candidates.

His offer of to debate Obama could also be campaign posturing before the June 12 vote. But it does put Ahmadinejad on record as supporting a potentially groundbreaking encounter following Obama''s offer for dialogue.