Iraqi Prime Minister Nouri al-Maliki said Monday no security agreement with the United States could be reached unless it included a "specific deadline" for the withdrawal of all American troops from Iraq.

Last week, U.S. and Iraqi officials said the two sides had agreed tentatively to a schedule which included a broad pullout of combat forces by the end of 2011 with a residual U.S. force remaining behind to continue training and advising the Iraqi security forces.

But al-Maliki's remarks Monday suggested that the Iraqi government is still not satisfied with that arrangement. An aide to the prime minister said Monday that Iraq remained adamant that the last American soldier must leave Iraq by the end of 2011 — regardless of conditions at the time.

The official, like others who spoke about the specifics of the debate, spoke on condition of anonymity because the text had not been approved by either government.

U.S. President George W. Bush has long resisted a timetable for pulling out troops from Iraq, even under heavy pressure from a nation distressed by American deaths and discouraged by the length of the war that began in 2003.

"There can be no treaty or agreement except on the basis of Iraq's full sovereignty," al-Maliki told a gathering of tribal sheiks. He said such an agreement must be based on the principle that "no foreign soldier remains in Iraq after a specific deadline, not an open time frame."

White House spokesman Tony Fratto said negotiations with the Iraqis continued, but reiterated the U.S. stance depended on conditions in Iraq.

"We're optimistic that Iraq and the U.S. can reach a mutual agreement on flexible goals for U.S. troops to continue to return on success — based on conditions on the ground — and allow Iraqi forces to provide security for a sovereign Iraq," he said in Crawford, Texas.

The Bush administration now speaks about "time horizons," but even that now appears unacceptable to al-Maliki's government.

"We find this to be too vague," a close al-Maliki aide told The Associated Press on Monday. "We don't want the phrase 'time horizons.' We are not comfortable with that phrase," said the aide, who spoke on condition of anonymity because of the sensitivity of the ongoing negotiations.

Another top al-Maliki aide, also speaking on condition of anonymity for the same reason, said the Iraqi government has "stopped talking about the withdrawal of combat troops. We just talk about withdrawals," including trainers and logistics troops.

In his Monday address, al-Maliki also suggested that the question of granting immunity to U.S. military personnel or contractors continued to be a sticking point in the negotiations.

In one key part of the draft agreement, private U.S. contractors would be subject to Iraqi law but the Americans are holding firm that U.S. troops would remain subject exclusively to U.S. legal jurisdiction.

Al-Maliki said Monday that his country could not grant "open immunity" to Iraqis or foreigners because that would be tantamount to a violating the "sanctity of Iraqi blood." He did not elaborate.

The agreement had been scheduled to be concluded by the end of last month.

No new date has been set, but the two al-Maliki aides said a final draft was now available to the political leaderships in Baghdad and Washington. One of the two said a breakthrough was not expected before next month.