TEHRAN, Iran -- Iraqi Prime Minister Nouri al-Maliki was in Tehran Saturday for talks that are expected to focus on a proposed U.S.-Iraq security agreement that Iran fears will keep the American military in neighboring Iraq for years.

Washington and Baghdad are also negotiating a parallel agreement to provide a legal basis for keeping U.S. troops in Iraq after the U.N. mandate expires at the end of the year.

The talks on the security plan are secret, and neither Baghdad nor Tehran has confirmed it would be addressed in al-Maliki's meetings. But ahead of the two-day visit, the prime minister's party sought to calm worries by insisting that the deal would not allow foreign troops to use Iraq as a ground to invade another country -- a clear reference to Iranian fears of a U.S. attack.

U.S. Congressional Democrats also have urged the Bush administration not to bypass Congress, which they believe should approve any deal. They fear a long-term security deal with Iraq -- if it committed the U.S. to protecting Iraq -- could make it difficult for the next president to withdraw U.S. forces from Iraq.

Hard-liners in Iran have warned that "the U.S.-cooked agreement turns Iraq into a full-fledged colony."

Yet, the toughest words have come from Iraqi officials, especially those loyal to Muqtada al-Sadr, the anti-American cleric whose militiamen fought U.S. and Iraqi troops in Baghdad until a May truce ended seven weeks of fighting. Tens of thousands took to the streets in Baghdad's Shiite slum of Sadr City on Friday to protest the agreement.

Its backers believe the deal would guarantee U.S. support as Iraq seeks to cement the security gains of the past year. It would also help assure Iraq's Sunni Arab neighbors, notably Saudi Arabia, that Iraq's Shiite-led government would not become an Iranian satellite.

U.S. officials have released no details about the negotiations, which began last March. But the U.S. alleges that Iran is encouraging a public campaign in Iraq against the proposed U.S.-Iraq security agreement, which the Iranians oppose.

Al-Maliki's Dawa party has described the talks as stalled, and prominent parliamentarians from Shiite, Sunni and Kurdish parties have written to Congress to express their opposition to the proposed agreement, which must be approved by the Iraqi legislature.

A lawmaker from al-Maliki's party told reporters Tuesday that the Iraqis and the Americans are far apart on the security agreement. Haidar al-Abadi said negotiations "are at a standstill, and the Iraqi side is studying its options."

Iranian state television broadcast comments made by Iraqi lawmakers and politicians who have denounced the proposed agreement as al-Maliki's plane touched down at Tehran's Mehrabad airport Saturday.

The official IRNA news agency said al-Maliki was expected to meet with Iranian Foreign Minister Manouchehr Mottaki and Intelligence Minister Gholam Hossein Mohseni Ejehi later Saturday. There were no immediate details about their talks.

Al-Maliki is also expected to hold separate talks Sunday with Iranian President Mahmoud Ahmadinejad, parliamentary speaker, Ali Larijani, and top nuclear negotiator Saeed Jalili, according to IRNA.

The news agency said al-Maliki will also discuss "security issues," a reference to U.S. allegations that Iran is arming, funding and training Shiite militiamen. Iran has denied the charges, saying it supports Iraq's security and stability.

The visit is the second by al-Maliki this year and comes three months after Ahmadinejad made a historic trip to Iraq.

Though both are Shiite-majority countries, Iran and Iraq were hostile to each other throughout Saddam Hussein's regime. Their eight-year war after Saddam invaded Iran in 1980 cost about 1 million lives.

But when Saddam's Sunni-dominated regime fell and Iraq's Shiite majority took power after the 2003 U.S.-led invasion, long-standing ties between the Shiites of both countries improved, though the two neighbors have yet to sign a peace treaty.