UNITED NATIONS — With thousands of demonstrators protesting outside that he had stolen Iran’s election, President Mahmoud Ahmadinejad stoutly defended his legitimacy here on Wednesday, declaring in a speech that the Iranian “people entrusted me once more with a large majority” in a ballot he described as “glorious and fully democratic.”
In a 35-minute address, Mr. Ahmadinejad leveled familiar attacks against the United States and delivered an oblique rant against Jews, saying it was unacceptable for a “small minority” to dominate the politics and economy of much of the world through “private networks.” But he did not raise the Holocaust, the subject of another anti-Semitic theme he has used in speeches.
Shortly before Mr. Ahmadinejad began speaking, the United States and other world powers met and announced that they would give Iran a chance to begin negotiating seriously over its nuclear program at a meeting on Oct. 1, or face consequences — harsher sanctions.
“They are at a turning point; they have a choice to make,” Secretary of State Hillary Rodham Clinton said after the meeting, which included foreign ministers from Russia, Britain, France, Germany and China. “We will now await the results of the Oct. 1 meeting and take stock at that time.”
While the statement issued by the countries did not appear to break new ground, senior American officials said it was significant because China and Russia had signed on to a strategy that explicitly warned Iran that there would be serious consequences if it was not prepared to negotiate.
Both countries have historically been reluctant to impose sanctions on Iran, with which they have extensive commercial ties. Obama administration officials also pointed to comments made by Russia’s president, Dmitri A. Medvedev, to President Obama in which he said Russia would consider sanctions.
Mr. Ahmadinejad, in an interview with Newsweek and The Washington Post, said Iran would consider permitting its nuclear experts to meet with scientists from the United States and other major powers to try to resolve concerns about its nuclear program. It was not clear what Mr. Ahmadinejad’s offer would entail or whether it could help resolve the standoff.
While American officials emphasized the progress they had made on Iran, Mrs. Clinton announced a shift in American policy toward another recalcitrant government, the military junta in Myanmar.
Speaking to a group of countries with ties to Myanmar, formerly known as Burma, Mrs. Clinton announced that the United States would begin engaging directly with Burmese officials after concluding that its longstanding policy of sanctions had not worked.
“We believe that sanctions remain important as part of our policy,” Mrs. Clinton said. “But by themselves, they have not produced the results that had been hoped for on behalf of the people of Burma.”
“Engagement versus sanctions is a false choice, in our opinion,” she added, “so going forward, we will be employing both those tools.”
She declined to discuss the level at which American engagement with Burmese officials would take place, though senior officials said the secretary herself was unlikely to meet with anyone.
Myanmar, however, is sending a minister to the United States next week, and a senior official said that by announcing this policy shift, Mrs. Clinton opened the door to some kind of meeting with that minister.
At the end of the meeting of foreign ministers on Wednesday, Foreign Secretary David Miliband of Britain read a statement indicating that the countries were united in their determination to present Iran with a clear choice.
There was similar solidarity outside the United Nations, where thousands of people from the Iranian diaspora massed to show their support for the democracy protesters in Iran, many carrying placards with a picture of Mr. Ahmadinejad and the message, “Not Iran’s President.”
Others carried pictures of young people who had been killed in Iran in demonstrations after the June election, some of whom had been tortured. Many wore green, which has become a symbol of the movement.
Hadi Ghaemi, the director of the International Campaign for Human Rights in Iran, who helped organize the protest, said Iranian expatriates wanted to send a strong message to Mr. Ahmadinejad that the world was “aware of the crimes that took place” since his re-election.
Nima Momeni, 25, an information technology consultant who traveled from Los Angeles for the rally, said he “could not bear the idea that Mr. Ahmadinejad could just come and address the General Assembly after the crimes that took place in Iran.”
Neil MacFarquhar and Sarah Wheaton contributed reporting.