UNITED NATIONS — Iran’s president accused “a few bullying powers” of trying to thwart his country’s peaceful nuclear program and declared in a speech today before the U.N. General Assembly that “the American empire” is nearing collapse.

President Ahmadinejad of Iran sharply attacked America and NATO, accusing them of acting as aggressors in Iraq and Afghanistan, and of starting those wars “in order to win votes in elections.”

“American empire in the world is reaching the end of its road, and its next rulers must limit their interference to their own borders,” Mr. Ahmadinejad said.

He reiterated Iran’s insistence that its nuclear program is purely peaceful, not aimed at producing nuclear weapons as America and some European countries allege.

“A few bullying powers have sought to put hurdles in the way of the peaceful nuclear activities of the Iranian nation by exerting political and economic pressures against Iran and also through threatening and pressuring the IAEA,” the U.N. nuclear watchdog.

America and its allies allege Iran wants to develop its uranium enrichment program to make nuclear weapons, while Tehran insists it is designed to produce electricity for civilian use.

Iran already is under three sets of sanctions by the U.N. Security Council for refusing to suspend uranium enrichment. Washington and its Western allies are pushing for quick passage of a fourth set of sanctions to underline the international community’s resolve.

Today, Mr. Ahmadinejad also lashed out at Israel, saying “the Zionist regime is on a definite slope to collapse, and there is no way for it to get out of the cesspool created by itself and its supporters.”

The Iranian president is feared and reviled in Israel because of his repeated calls to wipe the Jewish state off the map, and his aggressive pursuit of nuclear technology has only fueled Israel’s fears.

He said that six years after Saddam Hussein’s regime was ousted in Iraq, “the occupiers are still there.”

“Millions have been killed or displaced, and the occupiers, without a sense of shame, are still seeking to solidify their position in the … region and to dominate oil resources,” Mr. Ahmadinejad said.

In Afghanistan, terrorism is spreading quickly and the presence of NATO forces has contributed to a huge increase in the production of narcotics, Mr. Ahmadinejad said.

Mr. Ahmadinejad’s speech came just hours after President Bush made his eighth and final speech to the U.N. General Assembly, urging the international community to stand firm against the nuclear ambitions of Iran and North Korea.

“A few nations, regimes like Syria and Iran, continue to sponsor terror,” Mr. Bush said. “Yet their numbers are growing fewer, and they’re growing more isolated from the world. As the 21st century unfolds, some may be tempted to assume that the threat has receded. This would be comforting. It would be wrong. The terrorists believe time is on their side, so they’ve made waiting out civilized nations part of their strategy. We must not allow them to succeed.”

At one point during Mr. Bush’s 22-minute speech, Mr. Ahmadinejad turned to the Foreign Minister of Iran, Manouchehr Mottaki, and gave a thumb’s down.

During interviews ahead of his speech today, Mr. Ahmadinejad blamed American military interventions around the world in part for the collapse of global financial markets. He said the campaign against his country’s nuclear program was solely due to the Bush administration “and a couple of their European friends.”

“The U.S. government has made a series of mistakes in the past few decades,” Mr. Ahmadinejad said an interview with the Los Angeles Times. “The imposition on the U.S. economy of the years of heavy military engagement and involvement around the world … the war in Iraq, for example. These are heavy costs imposed on the U.S. economy.

“The world economy can no longer tolerate the budgetary deficit and the financial pressures occurring from markets here in the United States, and by the U.S. government,” he added.

In a separate interview with National Public Radio, Mr. Ahmadinejad claimed vast international support for his position and said the campaign consisted “of only three or four countries, led by the United States and with a couple of their European friends.”