"Such a summit needs certain preliminaries," he said, but did not give details.

"Discussions to set a date will continue, but are not related to a trilateral summit"

Mohammed Ali Hosseini, Iran foreign ministry spokesman

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The reports of a meeting came at a time when the White House is under increased pressure at home to approach Iran and Syria for help in Iraq. Such a measure is believed to be one of the recommendations by a panel on Iraq led by former Secretary of State James Baker.

An Iranian-Syrian-Iraqi summit would appear to fit into US hopes that Iraq's neighbors will step in to help stem the violence. Iran is believed to back Iraqi Shia militias blamed in sectarian killings that have killed thousands this year. Iran has denied the charges.

But Hosseini said Iran has already been active trying to support Iraq's security.

The Islamic Republic of Iran has been participating in providing security in Iraq and the region and will continue doing so," he said but did not elaborate. "Iran will discuss security with other countries including Syria, if necessary."

The spokesman confirmed that Iran has invited Syrian President Bashar Assad for an official visit to Tehran, the Iranian capital.

"Discussions to set a date will continue, but are not related to a trilateral summit," Hosseini said of the invitation extended to Assad.

Jalal Talabani, the Iraqi president, will visit Iran, the spokesman told journalists, but he did not say when. "

"His visit will be about cooperation between the two countries," Hosseini said.

Talabani was scheduled to visit Tehran on Saturday, on a trip that the Iranian side said last week was for bilateral talks. But the Iraqi president postponed his trip on Friday until Baghdad's airport - closed in a security clampdown - reopens.

Syrian officials have been silent about any plans Assad might have to travel to Iran, which is Damascus' only close ally.