BAGHDAD (Reuters) - Scores of U.N. arms teams combed at least four Iraqi sites for possible chemical, biological or nuclear weapons Monday, a day after they carried out a record 16 inspections.

Experts from the International Atomic Energy Agencydrove to al-Tuweitha compound, the main site of Iraq's nuclear program. The large facility, 12 miles south of Baghdad, has been inspected repeatedly in recent weeks.

Teams from the U.N. Monitoring, Verification and Inspection Commission (UNMOVIC) targeted at least three other sites, Iraqi officials said.

One group went to the Ibn Bitar research center some 6 miles north of the capital, they said. The facility belongs to the Ministry of Industry and Minerals.

Fares Abdul Kareem, head of the Ibn Bitar research center, told reporters: ``We are not producing anything related to the production of chemical or biological weapons. We are producing veterinary drugs for the treatment of animals.''

Another UNMOVIC team inspected a pesticide factory known as Fallujah-3, 54 miles northwest of Baghdad. Fallujah-3 was thought to have been linked to VX gas. It was heavily bombed while under construction during the 1991 Gulf War.

In the northern city of Mosul, two days after inspectors opened a permanent office there, the inspectors swooped into a free-trade zone in Faydah around 240 miles north of Baghdad. The zone is mainly for cross-border trade between Iraq and Turkey.

In an Army Day speech, Iraqi President Saddam Hussein issued a first public criticism of the inspections saying U.N. teams were carrying out intelligence work.

U.N. experts, absent for four years, have been working flat out since resuming inspections on Nov. 27 to check Baghdad's assertion that it has no banned weapons.

Sunday, U.N. arms inspectors paid a surprise visit to the complex housing Iraq's own weapons Monitoring Directorate (IMD), trapping Baghdad's U.N. envoy and a senior official inside for several hours.

They inspected a total of 16 sites across Iraq, their busiest day since returning in November.

The stepping up of inspections came three weeks before the inspectors were due to report back to the U.N. Security Council. Their report could determine whether a U.S.-led war with Iraq can be averted.

A U.N. Security Council resolution adopted in November gave Baghdad one last chance to disarm or face possible war. Iraq says it has no such weapons and no plans to produce them.