TEHRAN, Iran — Iraq’s prime minister made his first official visit to Iran yesterday, asking Tehran to prevent Al Qaeda militants from slipping across the border to carry out attacks, an Iraqi official said. Iran’s president promised to help Iraq establish security.

The visit by Prime Minister al-Maliki reflected the complex relationship between mostly Shiite Iran and Iraq’s government, dominated by Shiite allies of Tehran. Ties have grown stronger between the two, including new oil cooperation. But at the same time, the American government — the Iraqi government’s other top ally — has repeatedly accused Iran of interfering in Iraqi politics and allowing insurgents to cross the porous 1,000-mile border, claims that Iran denies.

A parliament member from Mr. Maliki’s Dawa Party, Haidar al-Obadi, said, “There are Al Qaeda members and Al Qaeda strongholds in Iran.”

He said the militants have been “taking advantage of the long border” to smuggle weapons and people into Iraq, “most likely without the Iranian government’s knowledge.”

“We ask Iran for cooperation in controlling the border to prevent any Al Qaeda exploitation of the border,” he told the Associated Press in Cairo, speaking in a telephone interview from Baghdad.

Tehran says it has no interest in fomenting instability across the border. Iran says that some Al Qaeda operatives may have illegally passed through Iran from Afghanistan months before the September 11, 2001, terrorist attacks, but it says it has arrested an unknown number of them. Al Qaeda’s branch in Iraq has carried out some of the most brutal suicide attacks against Iraqi Shiites.

Mr. Maliki, who lived in Iran during part of a long exile from Iraq during the rule of ousted leader Saddam Hussein, received a red-carpet reception at the presidential palace before talks with President Ahmadinejad.

Asked at a joint press conference following their talks about allegations that Iran was interfering in Iraq, Mr. Maliki said, “There is no obstacle in the way of implementing agreements between Iran and Iraq.”

“All our assistance to the Iraqi people will be to establish complete security in this country,” Mr. Ahmadinejad said, according to a state-run news agency report of the press conference. “Iran and Iraq enjoy historical relations. These relations go beyond from neighborly ties. Our relations will remain excellent,” Mr. Ahmadinejad said.

“This trip will strengthen bilateral relations. Iran and Iraq, as two brotherly neighbors, will stand by each other, and unwanted guests [American-led forces] will leave the region,” he said.