TEHRAN, Iran — President Ahmadinejad of Iran said yesterday that American political influence in Iraq is “collapsing rapidly” and said his government is ready to help fill any power vacuum.

The hard-line leader also defended Prime Minister al-Maliki of Iraq, a fellow Shiite Muslim who has been harshly criticized by American politicians for his unsuccessful efforts to reconcile Iraq’s Sunnis, Shiites, and Kurds.

“The political power of the occupiers is collapsing rapidly,” Mr. Ahmadinejad said at a news conference, referring to American troops in Iraq. “Soon, we will see a huge power vacuum in the region. Of course, we are prepared to fill the gap, with the help of neighbors and regional friends like Saudi Arabia, and with the help of the Iraqi nation.”

Mr. Ahmadinejad did not elaborate on his remarks, an unusual declaration of Iran’s interest in influencing its neighbor’s future. The mention of a Saudi role appeared aimed at allaying the fears of Saudi Arabia and other Sunni Muslim nations that Iran wants to dominate in Iraq. Even though Saudi Arabia and Iran have not cooperated in the past, it “doesn’t mean it can’t happen,” Mr. Ahmadinejad said.

Iran fought a brutal eight-year war with Saddam Hussein’s regime and welcomed the elimination of a deeply hated enemy. But Iran also strongly objects to the presence of America, another rival, over its eastern and western borders in Afghanistan and Iraq. “Occupation is the root of all problems in Iraq,” Mr. Ahmadinejad said. “It has become clear that occupiers are not able to resolve regional issues.”

President Bush defended the Iraq war in a speech at the American Legion’s national convention and accused Iran of violating human rights and trying to destabilize Iraq, Afghanistan and the wider region.

“Iran is sending arms to the Taliban in Afghanistan to be used to attack American and NATO troops,” Mr. Bush said. “Iran has arrested visiting American scholars who have committed no crimes and impose no threat to their regime. And Iran’s active pursuit of technology that could lead to nuclear weapons threatens to put a region already known for instability and violence under the shadow of a nuclear holocaust. Iran’s actions threaten the security of nations everywhere.” Mr. Bush and the American ambassador in Iraq have given blunt assessments of political stagnation in Baghdad, and Mr. Bush has said it is up to the Iraqi people to decide if their government deserved to be replaced.

But key Democratic politicians, including Senator Clinton, have called for Mr. Maliki to be replaced because his Shiite-dominated government has been unable to forge national unity.

Mr. Maliki has shrugged off the gloomy assessments of Iraq’s future, saying he would “pay no attention” to American critics and if necessary “find friends elsewhere.”

“They rudely say [the Iraqi] prime minister and the constitution must change,” Mr. Ahmadinejad said of American critics. “Who are you? Who has given you the right” to ask for such a change, he added.

Ousting Mr. Maliki, a longtime Shiite political activist, would require a majority vote in the 275-member Iraqi Parliament. As long as the Kurdish parties and the main Shiite bloc back Mr. Maliki, his opponents lack the votes for that.

In a move that could further strain American-Iranian relations, American troops raided a Baghdad hotel last night and detained about 10 people, including six whom an American-funded radio station described as members of an Iranian delegation visiting to negotiate contracts with the Iraqis.

The Iranian Embassy said seven Iranians — an embassy employee and six members of a delegation from Iran’s Electricity Ministry — were staying at the Sheraton Ishtar Hotel.

Iran has been vehemently protesting the detention of five Iranians by American troops in the northern Iraqi city of Irbil in January. American authorities have said the five included the operations chief and other members of Iran’s elite Quds Force, which is accused of arming and training Iraqi militants.

Iran describes the five, who remain in American custody, as diplomats.

Washington has accused Tehran of being behind attacks on American troops in Iraq — a claim Mr. Maliki’s government has only partially backed, saying Iran could have a role in the attacks. Iran has denied the charges.

Mr. Ahmadinejad dismissed the possibility of any U.S. military action against Iran, saying Washington has no plan and is not in a position to take such action.

As Mr. Ahmadinejad spoke, fighting between rival Shiite factions in southern Iraq raised new fears that a pullout by British troops there could lead to chaos. The clashes appeared to be part of a struggle for power of southern Iraqi Shiite heartland, which includes the bulk of the country’s vast oil wealth.