Iraq will not accept any security agreement with the United States unless it includes dates for the withdrawal of foreign forces, the government's national security adviser said on Tuesday.

The comments by Mowaffaq al-Rubaie underscore the U.S.-backed government's hardening stance toward a deal with Washington that will provide a legal basis for U.S. troops to operate when a U.N. mandate expires at the end of the year.

On Monday, Prime Minister Nuri al-Maliki appeared to catch Washington off-guard by suggesting for the first time that a timetable be set for the departure of U.S. forces under the deal being negotiated, which he called a memorandum of understanding.

Rubaie said Iraq was waiting "impatiently for the day when the last foreign soldier leaves Iraq".

"We can't have a memorandum of understanding with foreign forces unless it has dates and clear horizons determining the departure of foreign forces. We're unambiguously talking about their departure," Rubaie said in the holy Shi'ite city of Najaf.

He was speaking to reporters after meeting Iraq's top Shi'ite cleric, Grand Ayatollah Ali al-Sistani.

Rubaie said he spoke to Sistani about the U.S. talks, but did not say if the cleric had an opinion on the negotiations. The revered cleric is routinely briefed on key national issues.

"I informed the (clerical leaders) about some of the advances in the talks. There are real problems and difficulties, and we have many roadblocks ahead. There is a big difference in outlook between us and the Americans," Rubaie said.

The Bush administration has always opposed setting any withdrawal timetable, saying it would allow militant groups to lie low and wait until the 150,000 U.S. troops in Iraq left.

On Tuesday the White House said the talks were not aimed at setting a hard deadline for withdrawal.

"Negotiations and discussions are ongoing every day," White House spokesman Gordon Johndroe said in Japan, where President George W. Bush is attending a Group of Eight summit.

"It is important to understand that these are not talks on a hard date for a withdrawal."

PARLIAMENT HICCUP

In a further complication, Iraq's deputy parliament speaker Khalid al-Attiya said lawmakers must approve any deal the Iraqi government reaches and will probably reject the document if American troops are immune from Iraqi law.

It would be virtually unthinkable for the United States to allow its soldiers to be subject to Iraqi law.

Maliki's preference for a memorandum of understanding, which could be an attempt to bypass parliament, is in contrast to earlier talks which have all been leading to the signing of a formal Status of Forces Agreement (SOFA).

"Without doubt, if the two sides reach an agreement, this is between two countries, and according to the Iraqi constitution a national agreement must be agreed by parliament by a majority of two thirds," Attiya told Reuters in an interview.

Washington has SOFA pacts with many countries, and they typically exempt U.S. troops from facing trial or prison abroad.

Iraq said last week Washington was showing flexibility on some key issues, which officials said included dropping a demand for immunity for private contractors working for the U.S. government.

Control of military operations and airspace are other points of contention, along with the detention of prisoners.