NIAGARA FALLS, Ontario - The United States refused yesterday to accept hard-line President Mahmoud Ahmadinejad's claim of a landslide reelection victory in Iran and said it was looking into allegations of election fraud.

Any hopes by the Obama administration of gaining a result similar to Lebanon's recent election, won by a Western-backed moderate coalition, appeared to be in jeopardy.

"We are monitoring the situation as it unfolds in Iran, but we, like the rest of the world, are waiting and watching to see what the Iranian people decide," Secretary of State Hillary Rodham Clinton said at a news conference with Canada's foreign-affairs minister, Lawrence Cannon.

Minutes after Clinton spoke, the White House released a two-sentence statement praising "the vigorous debate and enthusiasm that this election generated, particularly among young Iranians," but expressing concern about "reports of irregularities."

Despite the challenge from reformist Mir Hossein Mousavi to Ahmadinejad, many officials and experts thought a Mousavi victory would result in only incremental shifts toward the United States.

Administration officials remained silent out of concern that any comments might influence the results. But they were privately hoping for a victory by the more moderate Mousavi.

President Obama's previous overtures include his recent address in Cairo to the Muslim world as well as, earlier, a televised New Year's address to the Iranian people and a series of diplomatic contacts. Officials say Obama's attempts to reach out have gone largely unanswered.

Neither Clinton nor the White House mentioned Ahmadinejad or Mousavi by name or acknowledged the incumbent's victory declaration.

Karim Sadjadpour, an Iran analyst at the Carnegie Endowment for International Peace, said yesterday that Ahmadinejad's claim of a victory put the Obama administration in a tough position.

"I think it's going to make it incredibly difficult for the Obama administration to acquiesce on Iran's enrichment of uranium when there is a president in Tehran who continues to deny the Holocaust and continues to be belligerent toward Israel," Sadjadpour said. "I don't see the probability of Ahmadinejad taking a more moderate or conciliatory approach his second time around. Similar to what President Bush said when he was reelected in 2004, he said, 'I've earned political capital, and now I am going to use it.' "

British Foreign Secretary David Miliband said concerns about ballot counting that candidates have expressed are an issue for Iranian authorities to address. "Our priority is that Iran engages with the concerns of the world community, above all on the issue of nuclear proliferation," he said.

Most countries appeared to be taking a wait-and-see approach, including China, Germany, Italy, and Japan - nations with strong economic ties to Iran.

France said it was closely following the situation.

About 200 Iranians protested outside the Iranian Embassy in London. Hadi Ghaemi, spokesman for the International Campaign for Human Rights in Iran, denounced the outcome as "a Tehran Tiananmen" - a reference to China's brutal 1989 crackdown on pro-democracy activists - and urged the international community not to recognize the result.