Weapons inspectors returned for the third straight day Monday to a huge complex where Iraqi scientists once worked on a nuclear bomb, while experts in Austria received the first samples sent by the U.N. team in Iraq.

Al-Qa'qaa, about 15 miles southeast of Baghdad, had been under U.N. scrutiny in the 1990s and was involved in the final design of a nuclear bomb before U.N. teams destroyed Iraq's nuclear program after the 1991 Persian Gulf War. It was one of at least six sites that inspection teams visited Monday morning.

During their Sunday visit to al-Qa'qaa, inspectors said a chemical team updated information about a sulfuric acid plant, an explosives production plant and storage areas. Sunday's inspection also focused on a production unit built between 1998 and 2002.

Also for the third day in a row, inspectors visited Hatteen, a complex some 40 miles south of Baghdad. Hatteen houses a number of government factories that produce everything from cars to ammunition.

"We do not have prohibited weapons at this site and all our activities are normal," Hussein Mohammed Khaled, Hatteen's director, told reporters after Monday's inspection. He said the inspectors took samples of aluminum bars from the facility and that the visit went smoothly.

In Austria, experts at a U.N. nuclear agency laboratory received the first samples gathered by inspectors in Iraq and planned to begin analyzing the material immediately.

Using electron microscopes, gamma and thermal ionization spectrometers and other tools, scientists at the lab outside Vienna will look for evidence that Iraqi President Saddam Hussein has a clandestine nuclear weapons program. Iraq denies it has any weapons of mass destruction.

An initial analysis will take two to three weeks, and the findings will be brought to International Atomic Energy Agency headquarters in Vienna for interpretation, Mark Gwozdecky, a spokesman for the U.N. agency, told The Associated Press. Eight samples were brought in Monday and another 20 samples were expected by the weekend.

The nuclear agency has said it hopes to have screening results from the first two dozen or so samples by the time its director, Mohamed ElBaradei, reports to the U.N. Security Council on Jan. 27.

The inspectors are working in Iraq under a Nov. 8 U.N. resolution that threatens serious consequences if Iraq fails to prove it has surrendered all its banned weapons. The United States has threatened to attack Iraq — alone if it deems it necessary — and says it has proof that Saddam is hiding weapons of mass destruction.

In Washington on Monday, White House spokesman Ari Fleischer said American officials were still studying a voluminous Iraqi declaration to the United Nations on Dec. 8 that reiterated Baghdad's contention it has no banned weapons.

Asked whether Iraq would have a chance to make good on any omissions that U.N. or U.S. officials find, Fleischer said it was made "abundantly clear from the U.N. that this was Iraq's last chance to inform the world in an accurate, complete and full way what weapons of mass destruction they possess."