The U.N. Security Council voted unanimously Thursday to extend the United Nations' mandate in Iraq for another year, but U.N. officials said it is still too dangerous to establish more than a small political mission in the country.

The resolution, which passed by a vote of 15 to 0, calls on the United Nations "to play a leading role" in assisting Iraq through its political transition. But U.N. Secretary General Kofi Annan cautioned in a report that the United Nations' role in Iraq would be limited, noting that the risk of violence "remains the overriding constraint" on U.N. activities there.

"For the foreseeable future the United Nations will remain a high value, high impact target for attack in Iraq," Annan wrote.

Annan's hesitancy poses a difficulty for the Bush administration, which has pressed the United Nations to broaden its presence in Iraq in advance of elections. It comes as U.S. and U.N. efforts to create a U.N. protection force to defend the organization upon its reentry into Iraq have stalled.

John C. Danforth, the U.S. ambassador to the United Nations, told reporters last week that the United States and its military allies would be prepared to provide security for U.N. staff members when they return. "The greater U.N. participation in Iraq, the better," Danforth said.

The bulk of the U.N. professionals working on Iraq -- about 50 -- will continue to manage humanitarian operations from Amman, Jordan, and Kuwait City. But Annan is sending a small political team headed by his new special representative, Ashraf Jehangir Qazi, to Baghdad this week to help prepare a national conference Sunday on the country's political future and pave the way for national elections in January.

It will be the first time the United Nations has had a permanent headquarters in Baghdad since the United Nations pulled out of Iraq in October 2003, after two suicide bomb attacks against its Baghdad headquarters. The bloodiest attack, on Aug. 19, 2003, killed 22 U.N. officials and associates, including Qazi's predecessor, Sergio Vieira de Mello of Brazil.

Iraq's three-day national conference is expected to draw about 1,000 delegates from Iraq's disparate political, religious and tribal groups to select a 100-member national council to oversee the country's interim government. The conference, originally scheduled for late July, was postponed after the United Nations voiced concern that key groups had refused to attend.

U.S. and U.N. officials have promoted participation in the conference as an opportunity for Iraqis to peacefully vie for political power.

"There's room in any democracy for people to participate peacefully," said State Department spokesman Adam Ereli. "That's what I think the national conference is all about. And that's what the work of the U.N., the work of the United States, the work of all of us is all about, is trying to move Iraq in that direction."