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TEHRAN, March 2 (Reuters) - Iranian President Mahmoud Ahmadinejad left for a landmark visit to Iraq on Sunday, saying the trip was designed to strengthen Iraqi security and expand economic ties between the neighbouring countries.

Ahmadinejad, accompanied by a delegation of ministers and senior officials, flew from a Tehran airport to make the first visit to Iraq by an Iranian president, a Reuters witness said.

The two countries fought a war in the 1980s that cost a million lives.

Ties have improved since U.S. forces toppled Saddam Hussein in 2003 but the United States has accused Iran of stoking violence in Iraq by backing Shi'ite Muslim militias. Tehran denies this.

"This trip is in line with strengthening peace between the two nations and regional countries. This trip is in the interest of regional nations," Ahmadinejad said at the airport.

"Our cooperation is in line with strengthening peace and security in Iraq and the region, and our cooperation with the Iraqi government is to establish security," he told reporters.

Ahmadinejad said the planned talks in Iraq would cover economic ties, expanding transport links, and boosting trade and energy cooperation between the two OPEC member countries.

(Reporting by Parisa Hafezi, writing by Edmund Blair, editing by Ralph Gowling)

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