Iraq will reject any security pact with the United States unless a specific date for withdrawal of US-led troops is set, Iraqi national security advisor Muwafaq al-Rubaie said in Najaf on Tuesday.

"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," al-Rubaie told reporters in the Shi'ite holy city.

As security conditions in Iraq improve, the Iraqi government's stance in negotiations with the US have become tougher. al-Rubaie's remarks were the toughest since the beginning of negotiations on a security pact between the two countries in March, analysts say.

Iraqi Prime Minister Nuri al-Maliki publicly announced Monday that his country was seeking a timeline for the withdrawal of US troops.

"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 their withdrawal," al-Maliki said during a meeting with a group of Arab ambassadors in Abu Dhabi, capital of the United Arab Emirates,

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

The security pact, also known as Status of Forces Agreement (SOFA), has to be signed by the end of July according to a declaration of principles agreed upon by US President George W. Bush and al-Maliki last November.

Some observers point out that the Iraqi government has hardened its position in recent days because it thinks the Bush administration is eager to sign an agreement before the November elections, which could give Iraq a chance to win a better deal.

The Bush administration has repeatedly rejected calls for any specific withdrawal timetable.

The White House responded to al-Maliki's comments Monday by saying the talks were aimed at reaching an agreement on a framework for future US-Iraqi relations rather than a "hard date" for US withdrawal from Iraq.

The US State Department also rejected Iraq's demand to set a timetable for a pullout, emphasizing that the withdrawal of its troops will be based on ground conditions.

"The US government and the government of Iraq are in agreement that we, the US government, we want to withdraw, we will withdraw. However, that decision will be conditions-based," State Department spokesman Gonzalo Gallegos said.

"We're looking at conditions, not calendars here," he said.

Apart from the difference of opinion on a specific withdrawal timetable, controversy in either country about the contents of a likely agreement has further complicated the ongoing talks.

Iraq's Deputy Parliament Speaker Khalid al-Attiya said any deal reached by the Iraqi government must be approved by deputies and the document will probably be rejected if American troops are immune from Iraqi law.

According to the Iraqi constitution, any national agreement needs to be approved by a two-thirds majority in parliament, he pointed out.

However, it seems unacceptable to the US to let its soldiers be subject to Iraqi law, analysts say.

Washington has SOFA pacts with many countries, which exempt US troops from trial or prison terms abroad.

Meanwhile, control of military operations and airspace, as well as detention of prisoners are all bones of contention between the two nations.