Iraqi Prime Minister Nouri al-Maliki said Saturday the U.S. decision to withdraw troops from Iraq by the end of 2011 came after his government refused to grant immunity from prosecution to U.S. troops in Iraq.

Mr. Maliki said the pull-out was according to schedule and that both sides were obliged to carry it out, but that any chance of extending the mission collapsed over the immunity issue. He noted Iraqi political factions rejected the notion of U.S. troops in Iraq working outside the country's laws.

The United States had asked for immunity for a small group of U.S. troops to remain in Iraq to help with training and counter influence of neighboring Iran. About 39,000 U.S. troops are currently stationed in Iraq, down from a high of about 165,000 in 2008.

Despite the impasse, U.S. Secretary of State Hillary Clinton on Saturday vowed that the withdrawal of troops will not end American commitment to Iraq.

Clinton, who is visiting Tajikistan, added that instead, the pullout marked a new phase of Washington's relations with Baghdad, and that the U.S. would continue to have a “robust” and “continuing” presence in the region.

Although the reaction in Iraq to news of the U.S. withdrawal was generally positive, some Iraqis said the American presence was still needed because the Iraqi army is weak and divided on sectarian lines.

U.S. President Barack Obama said Friday U.S. troops in Iraq would “definitely be home for the holidays.” Defense Secretary Leon Panetta said Washington will negotiate with Baghdad about a possible American role to train Iraqi forces.

About 150 U.S. troops will stay in Iraq after the end of the year, where some will be part of the U.S. embassy's security force — which is common at U.S. diplomatic posts worldwide.

The war, which began in March 2003, is one of the longest military conflicts in U.S. history. More than 4,400 U.S. troops have died in the fighting.