While weapons experts in New York and Vienna begin pouring over Iraq's 12,000-page weapons declaration, U.N. inspectors in Baghdad resumed their search for weapons of mass destruction. They revisited two sites, including a complex responsible for Iraq's former nuclear weapons research program.

The weapons inspectors returned to Iraq's al-Tuwaitha nuclear complex south of Baghdad where, in the 1980's, scientists worked to produce materials for a nuclear bomb.

It was the inspectors' second visit to Iraq's primary nuclear facility, after spending five hours at the complex last Wednesday. The inspectors want to make sure Iraq has not restarted programs aimed at building weapons of mass destruction.

Satellite photographs have reportedly shown new construction at the al-Tuwaitha complex, which was heavily bombed during the 1991 Gulf war. Israel bombed the facility's nuclear reactor in 1981.

The nuclear complex reportedly contains more than 100 buildings and the inspectors say they want to examine the contents of each and every one of them.

Meanwhile, a second team of inspectors revisited a plant west of Baghdad. That facility is suspected of having produced chemical and biological weapons.

Many of the inspectors were from a group of 25 that arrived Sunday in Baghdad. The U.N. teams also received the first of an expected eight helicopters that will allow them to make unannounced inspections virtually anywhere in Iraq.

The inspectors have visited about 25 facilities in Iraq since resuming their inspections November 27. They say they may want to investigate as many as 700 potential sites in a process that could take more than year.

On Sunday, an aide to Iraqi President Saddam Hussein, Amir al-Saadi, said Iraq may have been close to making an atomic bomb in the 1980s, but had not reached final assembly or testing. The official insisted Iraq has since quit efforts to build weapons of mass destruction, but U.S. and British officials say that is not true.

The officials say they have evidence regarding Iraq's nuclear, biological, and chemical weapons, but those officials have not yet revealed what information they have.