U.N. Secretary-General Kofi Annan says the United Nations will continue its work in Iraq. But he says U.N. officials are reassessing their security arrangements following the terrorist attack Tuesday at the United Nations' Baghdad headquarters that left at least 17 people dead.

Mr. Annan returned to New York to discuss the deadly blast in a special, closed door session with the Security Council. Prior the consultations, he again condemned what he described as the "senseless" killing of U.N. workers who were trying to help the Iraqi people, including top U.N. envoy Sergio Vieira de Mello.

The secretary-general said a new U.N. mission to Iraq, established in a recent Security Council resolution, will go ahead as planned. But he says U.N. officials are re-evaluating their security arrangements in Iraq. "Obviously, we are going to reassess certain things. It will be necessary, I am sure, to strengthen and reassess our security arrangements and that process has already begun," he said.

Mr. Annan made his remarks as questions are being raised about whether the United Nations turned down offers of protection from the U.S. and British-led coalition in order to maintain its independence. But Mr. Annan said decisions about security should not have been left to the protectorate.

Rather, he said the authority in charge of maintaining law and order in Iraq must make the crucial security-related decisions. "I do not know if the United Nations did turn down [an] offer for protection, but if it did, it was not correct and they should not have been allowed to turn it down," he said.

The secretary-general refused to assign blame for the deadly attack, but he said that "mistakes have been made" in Iraq.

He said sending a possible multi-national force to Iraq is under discussion, but the United Nations will not deploy its own peacekeepers, or so-called "blue helmets."

Mr. Annan would not name any candidates to replace his special representative, Mr. Vieira de Mello, who is being remembered, along with other victims of the attack, at United Nations offices around the world.