BAGHDAD — President Ahmadinejad of Iran today dismissed American accusations that his country is training extremists and demanded that the Americans withdraw from Iraq.

Speaking in a nearly hour-long news conference at the end of an unprecedented visit to Iraq, Mr. Ahmadinejad said American allegations — that Iran is training Shiite militants who target American troops and Muslim rivals — don’t matter to the Iranians.

“Of course American officials make such remarks and such statements, and we do not care … because they make statements on the basis of erroneous information,” the hard-line Iranian leader, who smiled through much of the session, said. “We cannot count on what they say.”

He said the foreign presence in Iraq was an “insult to the regional nations and a humiliation.”

Mr. Ahmadinejad is the first Iranian president to visit Iraq, and his two-day trip highlighted one of the unintended consequences for Washington after the 2003 American-led invasion of the Iraq that ousted Saddam Hussein from power.

Under Saddam, a Sunni who once led an eight-year war against Iran, the two countries were bitter enemies, but Iraq’s new Shiite-dominated government has deep ties to Iran’s cleric-led Islamic republic.

Mr. Ahmadinejad was warmly received by President Jalal Talabani, a Sunni Kurd, and other Iraqi leaders. He said Tehran and Baghdad are “brotherly” nations who share many beliefs and values.

“Of course, dictators and foreigners have tried to tarnish and undermine the emotional relations between the two states,” he said.

After meeting yesterday with Mr. Talabani, who told the Iranian leader to call him “Uncle Jalal,” Mr. Ahmadinejad drove through the American-controlled Green Zone to visit Prime Minister al-Maliki, a fellow Shiite, at his Cabinet offices.

The sprawling Green Zone contains the core of the American diplomatic mission to Iraq — including a massive new embassy — and is heavily protected against occasional rocket barrages. American officials have accused Iran of backing Shiite extremists behind such attacks.

“The presence of foreigners in the region has been to the detriment of the nations of the region,” Mr. Ahmadinejad said. “It is nothing but a humiliation to the regional nations.

“Their only achievements are that regional nations further dislike them, it adds to the regional nations’ hatred. No one likes them.”

Pressed by a reporter how he knows the Iraqis don’t like America, Mr. Ahmadinejad said that the “Iraqi people have been anti-colonialist and anti-occupation in the course of their history.”

“If you go to the streets and talk to ordinary Iraqi people, you will be able to realize the true nature of such a claim,” he said.

Still, the Iraqis are precariously balanced between America and Iran, with government officials saying in recent weeks that they don’t want the country torn apart in a power struggle between the two sides.

About 1,000 protesters in a Sunni-dominated neighborhood in Baghdad protested his visit today, a day after scattered demonstrations greeted his arrival. “Your mortars preceded your visit,” one placard read.

Though both Iraq and Iran have Shiite majorities, they were hostile to each other throughout Saddam’s long reign. About 1 million people died in the fighting that ensued after Saddam invaded Iran in 1980.

But when Saddam’s Sunni-dominated regime fell to the American-led invasion and Iraq’s Shiite majority took power, long-standing ties between the Shiites of both countries flourished.

Earlier today, Messrs. Talabani and Ahmadinejad signed seven memorandums of understanding on issues including industrial development, trade, and customs.