The chief U.N. weapons inspector said Friday he was sending a new, better-equipped team into Iraq to hunt out warheads unaccounted for by Baghdad.

In an interview broadcast on BBC Television, Richard Butler said the U.N. Special Commission he heads still is seeking answers from Iraq about biological and chemical weapons.Inspectors remain deeply concerned that Iraq is withholding information about its weapons of mass destruction, Butler said.

U.N. inspectors must certify that Baghdad has destroyed these weapons before punishing trade sanctions, imposed on Iraq after its 1990 invasion of Kuwait, can be lifted.

Butler said that special warheads "were loaded with chemical and/or biological agents that Iraq has not yet allowed us to adequately account for."

He added: "There is a technical team going into the field in a few days time with some new, special equipment that might be able to give an account of those warheads."

U.N. officials in Baghdad would say only that some warheads were unaccounted for, but declined to give specific numbers.

In the interview, which was monitored by The Associated Press in Baghdad, Butler pointed out that warheads are useful only when joined to missiles for delivery and said, "we have some remaining issues with respect to missiles that Iraq has not been able or willing to tell us the truth about."

He said that inspectors still were not satisfied that Baghdad has revealed everything about its chemical weapons, especially its ability to manufacture the lethal agent VX, and about "the black hole that is their biological program, about which they have never told us the truth."

Butler also complained about what he described as Iraqi attempts to silence him and his deputies.

In a letter to the United Nations made public Tuesday, Iraqi Foreign Minister Mohammed Saeed al-Sahhaf said U.N. Secretary-General Kofi Annan should punish any U.N. arms inspectors who speak to journalists about the hunt for Iraqi weapons.

"I am responsible for my organization," Butler said. "And I am responsible for public communication about it."

Butler also praised Annan's Feb. 23 accord to end a standoff over inspections at presidential compounds, which are now to take place with diplomatic escorts. "My job is to go out and test it in the field," Butler said of the accord.

An Annan envoy, Sri Lankan Jayantha Dhanapala, is in Baghdad organizing the diplomatic representatives for the teams.

The first palace inspections are expected later this month, U.N. officials in New York have said.

Dhanapala met Friday with the ambassadors or charge d'affaires from about a dozen of the embassies in Baghdad, including Algeria, China, Jordan, Iran, France and Pakistan.

In Baghdad, meanwhile, hundreds of Sudanese students demonstrated before the U.N. headquarters to protest against continued U.N. sanctions.

"We would like to draw the attention of U.N. secretary-general and world public opinion to the grave and serious conditions our Iraqi brothers are suffering because of the U.N. embargo," said Sudanese student Jalal Ziyada.

The demonstrators burned American, British and Israeli flags and an effigy of a snake that also carried an Israeli flag. They also strolled with a coffin covered with a U.S. flag written on it "Death to America."

"We will not give up two things, our (Arab) nation and Saddam Hussein," they chanted.

"We ask for the withdrawal of the U.S. and British troops from the Arab gulf as they cause lack of peace and security in the region," the letter read.