Balad, Iraq ? International weapons hunters crossed a threshold Saturday, paying their first visit under the new inspection program to a military post once declared “sensitive” and restricted by the Iraqi government.

On the third day of the renewed inspections, U.N. monitors arrived unannounced but received unrestricted access to the Chemical Corps base, as mandated by the U.N. Security Council when it sent them back to Iraq with greater powers to inspect anyplace, anytime.

Another team, meanwhile, inspected a complex that once was the heart of Iraq’s aborted effort to build nuclear bombs.

In both cases, as expected, the U.N. teams did not disclose their findings, holding them for later reports. But their spokesman indicated afterward they were satisfied with Iraqi cooperation. “They were able to conduct inspections as they planned,” Hiro Ueki said.

“They found nothing,” said the commander of the Balad military post north of Baghdad.

The inspections resumed Wednesday under a new Security Council resolution giving Iraq a “final opportunity” to shut down any chemical, biological or nuclear weapons programs, or face “serious consequences.”

Inspections in the 1990s, after the Gulf War, led to destruction of many tons of Iraqi chemical and biological weapons, and equipment to produce them. U.N. teams also dismantled Iraq’s nuclear weapons program before it could produce a bomb. But that inspection regime collapsed in 1998 amid disputes over access to sites and infiltration of the U.N. operation by U.S. spies.

Those inspectors believed they never found all the Iraqi weapons of mass destruction. The United States now threatens war to disarm the Baghdad government if the new inspections do not.

The 10 or so inspectors on Saturday spent almost five hours crisscrossing the small installation, paying close attention to what appeared to be crates of ordnance in open sheds, possibly large artillery shells, bombs or rockets. From beyond the barbed-wired fence, waiting reporters could hear the sound of a hammer and chisel prying open crates.

At times, inspectors wielded hand-held detectors of some kind. They also repeatedly consulted clipboards, apparently for checklists of the known contents of the base, home to an Iraqi battalion specializing in preparing the military to defend against chemical, biological or nuclear attack.

United Nations weapons inspectors leave an Iraqi military base near the town of Balad that once was declared a sensitive area by Iraq and which earlier required advance notice for inspectors to visit. The visiting inspectors Saturday reported they received unrestricted access to the site.

In the 1990s, Iraq declared some facilities to be “sensitive sites.” Under informal agreements with U.N. officials, advance notice was given of inspections at such sites and the number of inspectors was limited. Balad was one such site, Ueki said Saturday, but he didn’t know the circumstances of its prior inspection, sometime before 1998.

The new U.N. resolution overrides all such agreements and demands “immediate, unimpeded, unconditional, and unrestricted access” to all sites for the new inspection teams.

After the inspectors left, the base commander, an Iraqi colonel who wouldn’t give his name, said the U.N. experts had searched for chemical or biological weapons. “The inspection team arrived suddenly, searched, but they found nothing,” he said.

Another team of nuclear specialists, meanwhile, inspected two sites south of Baghdad, including Milad, formerly known as al-Furat, where Iraqi scientists and engineers in 1989-90 made progress in testing gas centrifuges, sophisticated technology that can “enrich” uranium for use in nuclear bombs.

Recent satellite reconnaissance found that a building planned for the centrifuges has been completed since the inspectors left in 1998. Asked whether Saturday’s inspection had covered that building, U.N. spokesman Ueki declined to answer. The nuclear team leader, Jacques Baute, has said previously, however, that it was highly unlikely the Iraqis had managed to resurrect a “full-blown” centrifuge program.