A homicide bomber, his body wrapped in explosives and his car filled with 50 pounds of TNT, struck a police checkpoint outside U.N. headquarters in Baghdad (search) on Monday, killing an Iraqi policeman who stopped him and wounding 19 people.

The bomber, who also died in the 8:10 a.m. blast, was trying to get into the U.N. compound at the Canal Hotel, where a truck bomb a month ago killed 23 people, including the top U.N. envoy to Iraq, Sergio Vieira de Mello (search), said a U.S. military spokesman. Monday's attack wounded two U.N. workers.

The attack, apparently timed to snarl attempts by Washington to win U.N. legitimacy for the U.S. occupation of this Arab country, could diminish the world body's willingness to become more deeply involved in Iraq's reconstruction. The United Nations already sharply reduced its work here after the Aug. 19 bombing.

Secretary-General Kofi Annan (search) warned that if the situation continues to deteriorate, U.N. operations in Iraq "will be handicapped considerably."

"I am shocked and distressed by this latest attack on our premises in Baghdad," Annan said at the United Nations.

"We are assessing the situation to determine what happened, who did it, and taking further measures to protect our installations," he said.

The blast, which could be heard over much of the Iraqi capital, took place a day before President Bush was to address the U.N. General Assembly. He was expected to seek an expanded U.N. role in rebuilding Iraq, a condition set by many nations for contributing peacekeepers and money to the reconstruction effort.

But it was unclear how the United States would respond to French and German requests for the world body to oversee the process of handing over more authority to Iraqis and to be given a larger role in the management of Iraq's transition to democracy.

Annan has said he wants assurances of security for U.N. personnel in Baghdad along with any expanded role.

The bomber in Monday's attack was blocked at a newly established police checkpoint on a street in back of the compound. As police inspected the bomber's car, he detonated the explosives.

In New York, Secretary of State Colin Powell called the attack "very regrettable," but noted that "the security guard did his job."

Praising new security arrangements around the hotel, a U.S. military officer at the scene credited Iraqi police with preventing an even greater tragedy.

"I reiterate that he was not through the checkpoint, and he was not near the U.N. compound. That means security is working," said Capt. Sean Kirley of the U.S. 2nd Armored Cavalry Regiment.

The bomb exploded about 200 yards from any of the buildings or mobile offices inside the compound and about 400 yards from the hotel building itself. The truck bomb last month was parked outside the front of the hotel just yards from Vieira de Mello's office, when it exploded and brought down the facade, trapping him and several others in the rubble.

Kirley said the Iraqi police had a warning of Monday's attack shortly before it happened. He did not give details.

The power of the blast sent the hood of the bomber's car flying 200 yards. The detached arm of a victim lay more than 100 yards away.

Iraqi police Master Sgt. Hassan al-Saadi, among the first on the scene after the explosion, said he was told by wounded policemen that a gray 1995 Opel with Baghdad license plates approached the entrance to the parking area.

"A guard went to search the car, opened the trunk, and the car exploded, killing him and the driver. When I arrived, there was fire and smoke, even the guard's body was ablaze," he said.

Authorities identified the slain policeman as 23-year-old Salam Mohammed.

An Iraqi workman who was slightly injured said he saw cars trying to enter the rear parking lot when one of them exploded.

"It was as if I was being pushed and thrown three meters (three yards) from where I was standing," the worker, Wissam Majid, said. "I saw fire and smoke. I started running away and then I lost consciousness."

The bomb exploded two days after an assassination attempt against Aquila al-Hashimi, one of three women on the Iraqi Governing Council and a leading candidate to become Iraq's U.N. ambassador if the interim government wins approval to take the country's U.N. seat.

She was reported to be improving Monday, after being shot in the abdomen by six gunmen who chased her two-car convoy as she left home. The Governing Council president, Ahmad Chalabi, blamed remnants of the regime of Saddam Hussein, whose government was toppled by U.S.-led forces in April.

Since Bush declared an end to major combat operations on May 1, more than 160 American soldiers have been killed. More than 300 U.S. soldiers have died in Iraq since the U.S.-led coalition launched military operations March 20.

The ongoing violence has raised questions about American stewardship of the country and has led to calls for an expanded role for the United Nations in post-Saddam Iraq.

U.N. officials contacted Monday refused to say how many foreign staffers remain in the country, citing security. At the time of the Aug. 19 attack, U.N. spokesman Fred Eckhard said there were about 300 international staff in Baghdad and more than 300 elsewhere in Iraq. These numbers are thought to have now been dramatically reduced.

Antonia Paradela, U.N. World Food Program spokeswoman, said Monday's bombing "worries us that the security situation is getting worse and that there are more incidents ... in the country and that our work might be hindered because of that."

In his U.N. speech Tuesday, Bush was expected to resist French and German pressures for a quick surrender of U.S. authority to Iraqis, aides to the president said.

His national security adviser, Condoleezza Rice, criticized any plans to rush the transfer of power, saying it must come in "an orderly process."

"The French plan, which would somehow transfer sovereignty to an unelected group of people, just isn't workable," she told reporters.

According to diplomats familiar with early drafts and discussions, a draft Security Council resolution backing a multinational occupation force, circulated by American officials, won't specifically meet French demands for a timetable on the handover.

It will instead call on the 25-member U.S.-picked Iraqi Governing Council to come up with a timetable of its own -- a compromise that may satisfy the French only if a framework for such a timetable is agreed upon privately beforehand.

Diplomats said U.S. officials were talking with European allies to work out the pace of any handover of authority to the multinational occupation force.