ISLAMABAD - Pakistan shut schools and colleges nationwide on Wednesday a day after a suicide attack on a prestigious Islamic university as ground troops pressed home an anti-Taliban offensive.

Pakistan went on heightened alert against attacks from Al-Qaeda and Taliban extremists after a month of carnage that has left around 185 people dead in the nuclear-armed Muslim power bordering Afghanistan.

Millions of students faced disruption as the federal and provincial governments, along with private school associations and the military, decided to close schools, colleges and universities.

Some schools shut earlier this week and the rest of the country followed suit after two suicide bombers Tuesday blew themselves up at Islamabad's International Islamic University, killing five people.

"There are around 414 schools, colleges and universities run by the federal government. All have been closed because of security threats received in recent days," education ministry spokesman Atiqur Rehman told AFP.

"Similar orders have been issued by the four provincial governments. We will assess the situation and hopefully they will reopen on Monday," he added.

"It is unfortunate and frustrating for parents. We are taking precautionary measures.

"We cannot depute police at every school. We hope principals and heads of institutions will make proper security arrangements."

Pakistan's cabinet was in talks Wednesday and Interior Minister Rehman Malik was to convene a separate meeting to discuss long-term security measures to protect students and reassure panicked parents.

"We are under constant threat. Our children's education is suffering. If they can attack an Islamic university, they can do it anywhere," said Muhammad Irfan, whose five-year-old attends one of Islamabad's top private schools.

"We don't know what to do. We can't sacrifice our children but neither can we keep them at home."

Roads outside schools were deserted as tense staff mobilised private security guards to beef up security.

Tuesday's university bombing was the seventh major militant attack in just over a fortnight, and the first since the military launched what officials vowed would be a knock-out blow against the Taliban in South Waziristan.

Two explosions seconds apart rocked a male teaching faculty and women's cafeteria of what is one of the largest Islamic universities in the world, attracting Muslim students from home and abroad.

The attack came after a raid on army headquarters left 23 people dead and five UN World Food Programme workers were killed when a suicide bomber dressed in military uniform detonated his explosives in their Islamabad office.

Authorities believe that many of the bombings in Pakistan, as well as attacks in the West, are being planned by Al-Qaeda and Taliban militants in the lawless tribal region of South Waziristan.

Officials say at least 105 militants and 13 soldiers had been killed since the military offensive began on Saturday in the semi-autonomous region, and more than 120,000 civilians have now fled the war zone.

Difficult terrain, mines and fierce clashes have slowed Pakistan's advance and officials admit the offensive could take longer than expected.

There have been heavy clashes on the heights overlooking Kotkai, the home town of Pakistani Taliban chief Hakimullah Mehsud and Qari Hussein, a reputed suicide bomb trainer.

Numerous previous offensives in the tribal belt have had limited success, costing the lives of 2,000 troops and ending generally with peace agreements that critics say gave the insurgents a chance to re-arm.