BAGHDAD - The surge of U.S. forces has driven down insurgent attacks in Baghdad but violence elsewhere in Iraq raises questions about whether killings will continue to drop as American forces begin to leave, the United Nations said Saturday.
As security improved in Baghdad, violent attacks spread last year to other parts of the country, including Diyala Province and Mosul, al-Qaida's last urban stronghold, according to the report from the United Nations Assistance Mission for Iraq.
"The government of Iraq continued to face enormous challenges in its efforts to bring sectarian violence and other criminal activity under control against a backdrop of political instability," the report said.
The U.S. military has said a 60 percent reduction in attacks followed the surge.
"This is a window of opportunity for Iraq," Staffan de Mistura, the U.N. chief in Iraq, said at a news conference in Baghdad.
The U.S. military in Iraq did not immediately respond to requests for comment.
Thousands of U.S. forces went sent to Iraq starting last year as part of a strategy by Gen. David Petraeus, the commander of U.S. forces in Iraq, to secure the capital and give Iraq's politicians breathing room to cut deals that would bring minority Sunni Arabs into the government and weaken the insurgency.
De Mistura said so-called Awakening Councils, groups of Sunni former fighters who have accepted U.S. backing to fight al-Qaida in Iraq, also have played a role in reducing violence.
But the U.N. report cautioned against concluding the surge was a success because "the extent to which the decrease in violence was sustainable remained unclear." And violent attacks have grown more frequent in recent weeks.
Twelve U.S. soldiers have been killed in the last week, five of them in a single suicide attack in central Baghdad. A week ago two massive bombs hit Baghdad's Karradah neighborhood, killing 68 people.
On Saturday, Iraqi security forces clashed with a breakaway faction of Shiite cleric Muqtada al-Sadr's Mahdi Army in Kut, leaving five dead and 15 wounded, police said on condition of anonymity because they were not authorized to release information.