El Paso, Texas (CNN) -- A brigade of U.S. troops originally scheduled to be among the very last to leave Iraq is being pulled out of the country months ahead of its planned departure, military officials said Saturday.





The announcement follows news this month that a deal to keep American troops in Iraq past a December 31, 2011, deadline to withdraw was on shaky ground after Iraqi leadership said any remaining U.S. forces would not be granted immunity from Iraqi prosecution. Secretary of Defense Leon Panetta and other top brass have repeatedly said any deal to keep U.S. troops in Iraq beyond the withdrawal deadline must require a guarantee of legal protection for American soldiers.





The Fourth Brigade Combat Team, First Armored Division, based at Fort Bliss, deployed to Iraq in August to replace two withdrawing brigades. The troops were sent with the understanding they would be among the last to leave the country and were told to expect up to a 12-month deployment, though it wasn't clear how long they would stay in Iraq. But brigade officials informed hundreds of military families gathered Saturday at its headquarters that their troops would begin returning home within weeks.





When family members inquired why soldiers were returning early, they were told by a military official: "Basically, what's happened ... is that the United States and Iraq have not come to an agreement," according to a CNN reporter who attended the meeting.





Additionally, the brigade official told families: "We were over there for a couple of missions. Those missions are finished."





A U.S. military official in Iraq, speaking on condition of anonymity, confirmed to CNN Saturday the early withdrawal of this brigade, citing a number of possible reasons, including the lack of a deal on the legal immunity issue and the fact that the State Department is "standing up" its operations faster than expected.





When the United States and Iraq agreed in 2008 to a withdrawal deadline, the two countries also signed off on a Strategic Framework Agreement that calls for a long-term bilateral relationship. As part of that agreement, the State Department is deploying thousands of workers to Iraq to take over where military officials leave off in their dealings with the Iraqi government.





U.S. officials in Washington on Saturday declined to comment on reports that troops were being withdrawn ahead of schedule or because of a breakdown in negotiations, except to say the United States is committed to withdrawing all troops by the December 31 deadline.





"At the same time we're building a comprehensive partnership with Iraq under the Strategic Framework Agreement including a robust security relationship, and discussions with the Iraqis about the nature of that relationship are ongoing," said Tommy Vietor of the National Security Council.





Pentagon spokesman George Little also dismissed reports of a breakdown in talks with Iraqis, saying "Suggestions that a final decision has been reached about our training relationship with the Iraqi government are wrong. Those discussions are ongoing."





Officials at Fort Bliss said the brigade's return is in line with the U.S. planned departure.





"In the process, we are bringing troops back home to meet the December 31st agreed-upon deadline," said Lt. Col. Dennis Swanson, a public affairs officer for the First Armored Division.





When asked about the legal immunity issue, Major Gen. Dana J. H. Pittard, commander at Fort Bliss, said, "We're going to do what's right by our soldiers."





"We shouldn't see American soldiers in Iraqi courts on trumped-up charges," he said.





His comments echo recent statements by Panetta and U.S. Army Chief of Staff Raymond Odierno.





Panetta said last week that negotiations over the legal immunity issue are ongoing between Iraq's political leadership, U.S. Ambassador James F. Jeffrey and Gen. Lloyd J. Austin III, commander of U.S. forces in Iraq. The meetings include discussions about the rights of American troops and what will be required in order for those troops to assist Iraqi forces in the future, according to Panetta.





"If you're going to play a large role in dealing with another country where it requires, as I said, a large group of troops to be on the ground
originally scheduled to be the last to leave? who says talks are ongoing when was it scheduled to leave who has not agreed
A brigade of U.S. troops Panetta December 31, 2011, Secretary of Defense Leon Panetta and other top brass
question: originally scheduled to be the last to leave?, answer: A brigade of U.S. troops | question: who says talks are ongoing, answer: Panetta | question: when was it scheduled to leave, answer: December 31, 2011, | question: who has not agreed, answer: Secretary of Defense Leon Panetta and other top brass