"Our stance in the negotiations with the Americans will be strong. We will not sign any memorandum of understanding without specifying a date for the withdrawal of foreign troops from Iraq," Rubaie told reporters in Najaf.

Rubaie's comments came after his meeting with Shiite cleric Grand Ayatollah Ali al-Sistani, during which Rubaie briefed him on the progress of his government's security efforts and the ongoing talks over the security agreement with the United States.

Rubaie's new strong remarks also came a day after Iraq's Prime Minister Nuri al-Maliki said that his country was seeking a timetable for the withdrawal of US troops as part of its negotiations with the United States on the status of US forces in Iraq beyond 2008.

"The current trend is to reach either a memorandum of understanding for the departure of the troops, or a memorandum of understanding for setting a timetable for its withdrawal," Maliki said during a meeting with a group of Arab ambassadors in Abu Dhabi, capital of the United Arab Emirates, a day before ending his visit to the Gulf country.

However, the United States immediately rebuffed Maliki's comments, saying that its talks with Iraq on future US-Iraq relations will not include a date for the US troops to withdraw from the Middle East country.

"It is important to understand that these are not talks on a hard date for a withdrawal," White House spokesman Scot Stanzel said.

"As (US) Ambassador (Ryan) Crocker has said, we are looking at conditions, and not calendars -- and both sides are in agreement on this point," Stanzel added.

Baghdad and Washington are currently holding talks aimed at reaching a deal on a continued US military presence in Iraq after a UN mandate expires in December.

US President George W. Bush and Maliki agreed on a declaration of principles last November to sign a Status of Forces Agreement (SOFA) by the end of July that would decide the future presence of US troops in Iraq and long-term bilateral economic, political and security relations.

Last week, Iraq's Foreign Minister Hoshyar Zebari said that the United States had shown flexibility in negotiations with Iraq on the security pact.

However, Zebari warned that if his country fails to sign a strategic framework agreement with the United States, it will be obliged to demand an extension for the UN mandate until the country builds its own security forces.