BAGHDAD, Iraq — Gunmen dressed as police commandos kidnapped up to 150 staff and visitors in a lightning raid on a Baghdad research institute Tuesday, the largest mass abduction since the start of the U.S. occupation. Three of those taken were later released.

Iraq's higher education minister immediately ordered all universities closed until security improvements are made, saying he was "not ready to see more professors get killed.

"I have only one choice which is to suspend classes at universities. We have no other choice," Abed Theyab told parliament. Theyab said he had repeatedly petitioned for more university security from the ministries of Defense and Interior, who command the police, but had received none.

Alaa Makki, head of the parliament's education committee, interrupted the body's session to say that between 100 and 150 people, both Shiites and Sunnis, had been abducted in the 9:30 a.m. raid.

He urged the prime minister and the defense and interior ministers to respond rapidly, calling the abductions a "national catastrophe."

The mass kidnapping is the largest since about 50 people taken from the offices of a private security company in March. Their fate remains unknown.

"It was quick operation. It took about 10 to 15 minutes," Theyab said. "It was a four-story building and the gunmen went to the four stories." He said the gunmen had at least 20 vehicles, but possibly many more.

Makki said the gunmen had a list of names of those to be taken and claimed to be on a mission from the government's anti-corruption body to check on security ahead of a planned visit by the U.S. ambassador. Those kidnapped included the institute's deputy general directors, employees, and visitors, he said.

Police and witnesses said the gunmen, who numbered about 80, had closed off streets surrounding the Ministry of Higher Education and Scientific Research, Scholarships and Cultural Relations Directorate in the downtown Karradah district. The institute is responsible for granting scholarships to Iraqi professors and students wishing to study abroad.

The facility appeared to be an easy target for the kidnappers, whose motives remain unknown. Police spokesman Maj. Mahir Hamad said four guards put up no resistance and were unharmed.