Iraqi Prime Minister Nouri al-Maliki says the U.S. decision to withdraw troops from Iraq by the end of the year came after the Iraqi government refused to guarantee legal immunity for U.S. service members in Iraq.

Mr. Maliki spoke to reporters Saturday, a day after U.S. President Barack Obama announced the withdrawal. 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 remain in Iraq, down from a high of about 165,000 in 2008.

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

Clinton said the pullout marks a new phase of Washington's relations with Baghdad. She said the U.S. would go on to have a “robust” and “continuing” presence in the region.

Clinton commented from Tajikistan, a stop on her tour of Central Asia.

Mr. Obama said Friday that U.S. troops in Iraq would “definitely be home for the holidays.” He said he and Mr. Maliki were in agreement on that decision.

U.S. Defense Secretary Leon Panetta said later Friday that the United States will negotiate with the Iraqi government after the end of 2011 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.

Before Friday's announcement, the possibility had remained that U.S. troops would extend their presence in the nation beyond the December 31 deadline set in 2008.

The war, begun 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 conflict.