Gunmen in military-style uniforms have abducted scores of staff and visitors from a government building in Baghdad.
The building appears to have been a soft target for kidnappers
The attackers stormed the education ministry's research department, locked women in a room and took the men away.
Some 20 hostages have been found and officials now say they think up to 50 people in total were abducted.
Security forces have surrounded areas where they believe people are being held, officials say, while five senior police officers have been arrested.
These include the police chief of the Karrada area where the abductions took place.
Initially, Iraqi officials said more than 100 people had been kidnapped but the prime minister's office later revised that figure.
"No-one can give an exact figure since the number of employees in the building was about 70," a spokesman at the education ministry told the Associated Press news agency.
It is the latest attack to target Iraq's academics, who are increasingly fleeing the country in the face of the violence.
Correspondents say many Iraqis believe mass kidnappings like this latest incident are committed by members of the Shia Muslim-dominated security forces or take place with their collusion.
Such kidnappings are often for ransom, but many victims are subsequently found dead.
Higher Education Minister Abd Dhiab ordered all Baghdad's universities to close until the security situation improved.
In other developments:
- A blast at Baghdad's Shurja market killed 10 people and wounded 25, police said
- An overnight US raid killed six people in mainly-Shia east Baghdad, sparking angry anti-US protests
- Thirty died in a US raid on the Sunni stronghold of Ramadi, Iraqi officials said
- Police found 11 bodies with gunshot wounds in Mosul, while 10 kidnap victims were found shot dead in Baquba
The head of the parliamentary education committee, Alaa Makki, interrupted a televised parliamentary session with the news of the mass abduction.
He urged the prime minister and interior and defence ministers to respond rapidly to what he called a "national catastrophe".
Mr Makki said the abductees had been both Shias and Sunnis and had been seized by gunmen claiming to be working for the government's anti-corruption body.
However, a civil servant who said he was returning to the building at the time of the abduction, described gunmen lining up the male staff in the car park and checking their identity cards.
"They picked only the Sunni employees. They even took the man who was just delivering tea," he told Reuters news agency
"They gathered them all in the pick-ups. At the same time, I saw two police patrols watching, doing nothing," he said.
The gunmen reportedly closed off roads around the institute and took away their captives in handcuffs.
The institute is responsible for awarding grants to Iraqi academics wishing to study abroad.
Academic institutions have been particularly badly hit in the violence that has engulfed Iraq since the US invasion in 2003, with dozens of professors killed and hundreds leaving the country because of fears for their safety.