Iranian President Mahmoud Ahmadinejad is to head to Afghanistan on Wednesday, his first trip to Tehran's eastern neighbor since the re-election last August of his counterpart Hamid Karzai.

"The president is going on Wednesday to Afghanistan", foreign ministry spokesman Ramin Mehmanparast told reporters at his weekly press conference.

On Sunday, an Iranian news agency, Mehr, reported that Ahmadinejad was to make a one-day trip to Kabul on Monday to hold talks with Karzai on the challenges facing war-torn Afghanistan.

But an official at Ahmadinejad's office later denied the timing.

Ahmadinejad and several Iranian officials have repeatedly called for the withdrawal of U.S.-led forces from Afghanistan, saying their presence was stoking the Taliban insurgency.

But despite their rivalry, Washington and Tehran are both sworn enemies of the extremist Sunni Muslim militia which ruled in Kabul from 1996, before being overthrown in the 2001 U.S.-led invasion.

The United States has made a number of efforts to involve all of Afghanistan's neighbors, including Iran, in restoring stability to the country.

But they have been complicated by the lack of diplomatic relations between Tehran and Washington, and the standoff over Iran's controversial nuclear program.

Shiite Iran, which has close ethnic and religious ties with Afghanistan, has long suffered from the effects of opium production in its neighbor, with easily available heroin fueling a big rise in drug use at home.

Afghanistan is the source of 90 percent of the world's heroin.