As many as 80 armed men took part in the morning attack, which netted academics, employees and visitors to the ministry of higher education's scientific research, scholarships and cultural relations directorate, situated in Baghdad's relatively peaceful Karrada district.

There was some confusion tonight over the number of victims. Initial reports suggested 150 had been taken. This was later revised down to 130, while the prime minister's office put the number between 45 and 50.

Major General Jalil Khalaf, the interior ministry spokesman, said those arrested included the police chief for Karrada. Also held were the commander of the police brigade in charge of the area and three other officers, he added. The gunmen were wearing interior ministry commando uniforms specifically designed to prevent counterfeiting.

"It's a terrorist act," said Abed Dhiab, the minister for higher education. "They kidnapped more than 100 employees and visitors." The victims include Sunnis and Shias, he added.

According to police sources and witnesses, the gunmen arrived in more than 20 pick-up trucks and sports utility vehicles and sealed off the approaches to the building. Several cars approached the ministry's checkpoint and reportedly told guards they were part of an advance group from the interior ministry conducting a security sweep ahead of a visit by the US ambassador to Iraq, Zalmay Khalilzad.

Once inside the four-storey building, however, they rounded up men and women into separate rooms and took their mobile phones. The men, including senior academics, guards and visitors, were handcuffed and loaded on to the back of the pick-up trucks and driven off. The operation, which began at about 9.30am (0730 GMT), was over in 15 minutes.

Three of the hostages were later reported to have been freed nearby. The gunmen were reported to have headed toward the Shia stronghold of east Baghdad.

Insurgents, criminal gangs, and militias have frequently carried out attacks while posing as Iraqi security officers, and the security forces themselves have been heavily infiltrated.

The interior ministry, which is controlled by the ruling Shia alliance, repeatedly denies having links to the death squads and militias blamed by Sunnis for instigating sectarian violence and kidnappings. A senior, non-Shia interior ministry source told the Guardian today: "In truth we don't know whether the kidnappers were terrorists, militias, criminals, or interior ministry renegades. Whatever the explanation, it will do nothing for people's trust in us."

In response, Mr Dhiab ordered the suspension of all academic programmes and the closure all universities, though he later appeared to pull back from a full shutdown. "I have only one choice, which is to suspend classes at universities' because I am not ready to see more professors get killed," he told parliament.

The minister, a member of a leading Sunni party, also accused Iraq's security chiefs of ignoring repeated requests to beef up security around educational institutions following a series of threats.

Since the US invasion in 2003, Iraq's academic institutions and staff have come under regular attack from insurgents and religious extremists. Scores of senior academics have been killed or assassinated and thousands more threatened.

Adnan Pachachi, an Iraqi politician and ex-governing council member, said: "There is evidence of a systematic and very sad attempt to drain Iraq of its brains."

· Additional reporting from Salaam Jihad, Baghdad