June 11 (Bloomberg) -- The U.S. troop surge in Baghdad is failing, according to a report by United Nations Secretary- General Ban Ki-moon that said the heavily fortified Green Zone in the Iraqi capital has become too dangerous for his staff.

``Insurgent attacks persist and civilian casualties continue to mount,'' Ban said in a quarterly report to the UN Security Council. ``While there was a brief lull in the level of sectarian violence early in the reporting period, it now appears that militia forces are resuming their activities.''

Five additional U.S. brigades have deployed to Iraq since the start of the year in an attempt to intensify security against sectarian violence and attacks on Iraqi and coalition forces, taking the total number of U.S. troops in the country to about 150,000.

Last month was the deadliest for U.S. forces in Iraq since the November 2004 battle for Fallujah, with more than 120 killed. Some 3,491 U.S. military personnel have died in Iraq, of which 2,864 were killed in action since March 2003, according to the Department of Defense.

``Despite the efforts of the Iraqi and multinational security forces to stem violence, progress was slower than had been hoped when security initiatives were launched at the start of 2007,'' Ban said. ``This has been demonstrated by continued attacks on the civilian populations.''

`Unacceptable Risks'

Ban said the UN headquarters within the Green Zone was deemed not safe enough and, given the ``unacceptable security risks,'' staff there have moved into ``more hardened'' facilities while a new building is built. A curfew and limits on travel inside the Green Zone have been imposed on UN workers, he said.

The central Baghdad Green Zone, which houses foreign embassies and government buildings, is protected by U.S. forces and private contractors. It is surrounded by high concrete blast walls and all entry points are staffed by security guards. Ban said the ``major development'' in Iraq in the past three months was the increase in mortar and rocket attacks on the Green Zone, to 39 in the first 22 days of May from 17 in April.

Ban said the partial British pullout from the southern city of Basra caused the UN to reduce its staff of about 10 and move them to a more secure headquarters in the nearby military air base.

The UN, which has about 130 international workers in Iraq, won't increase that number now, Ban said in the report. He asked the Security Council and Iraqi government to provide ``clear direction'' on what the UN should do, while also saying that ``creation of necessary infrastructure and operational conditions'' are required.

Ban said the humanitarian situation is deteriorating, with up to 50,000 Iraqis fleeing their country each month and 765,000 primary-school age children, 17 percent of the total, not attending school.

To contact the reporter on this story: Bill Varner in United Nations at wvarner@bloomberg.net.

Last Updated: June 11, 2007 13:46 EDT