The U.S. military has advised Iraqi authorities that it will have to shut down security and service operations in Iraq if the year ends without a security agreement or a renewed U.N. mandate for American forces, Iraqi officials said Monday.

Iraqi politicians are considering a draft agreement that would keep U.S. troops in Iraq through 2011 and give the Iraqis a greater role in security operations.

If parliament does not approve the deal before the U.N. mandate expires Dec. 31, there will be no legal basis for the U.S. to operate in Iraq.

But some key Shiite politicians say the agreement cannot win approval in its current form and have asked for unspecified changes.

Kurdish lawmaker Mahmoud Othman said the U.S. had submitted papers identifying a number of activities that would stop at the end of the year in the absence of a legal framework. These include not only security operations but also infrastructure improvements and assistance to ministries.

"This is an obvious attempt at blackmail," Othman said. "The aim of this kind of pressure on the Iraqi government is unacceptable. Such measures while the negotiations are still continuing might backfire."

Iraq's Sunni Vice President Tariq al-Hashemi told McClatchy News Service that the top U.S. commander in Iraq, Gen. Ray Odierno, listed "tens" of areas that faced cutoff in a three-page letter that al-Hashemi called "really shocking for us."

The Associated Press was unable to contact al-Hashemi for comment. Odierno's spokesman, Lt. Col. James Hutton, said there was no letter but "we provided information as a part of our normal engagements with many in the government of Iraq."

He would not elaborate.

But Sadiq al-Rikabi, a senior aide to Prime Minister Nouri al-Maliki, said U.S. and Iraqi officials had repeatedly discussed what operations would be impacted if the Americans lose their legal authority in Iraq.

Iraqi government spokesman Ali al-Dabbagh said that without a ratified agreement or a new U.N. mandate "there will be no legal cover for the U.S. military presence here, which means they will have to suspend their operations."

"We are trying to avoid reaching that point," he said. "We don't want a legal vacuum. The American administration is just as concerned about Iraq's security as we are."

The Kurdish alliance, which holds 54 of the 275 parliament seats, has expressed support for the agreement. Followers of anti-American Shiite cleric Muqtada al-Sadr, who control 30 seats, have rejected any pact with the U.S.

Most of the other major parties, however, have not taken a formal position on the agreement although several politicians have said the draft needs unspecified amendments in order to win approval.

Al-Maliki has said he won't submit the draft to parliament unless he is confident of broad support.