Deadly clashes pitting army troops and police against protesters rocked Cairo's political centre for a third day, widening divisions over the military's handling of transition from Hosni Mubarak's rule.

At least 10 people were killed in the violence that also destroyed a historic library housing priceless national archives.

Armed forces detained 164 people including minors, a military source said, as street battles raged outside parliament and government offices where protesters have been demanding an end to military rule.

The latest clashes erupted on Friday, overshadowing a vote count in a multi-stage parliamentary election, the first since Mubarak was ousted from power after three decades of rule.

Demonstrators hurled stones and pieces of metal over a concrete wall erected by troops on a wide avenue leading from Tahrir Square to the seat of government, AFP journalists reported.

By afternoon, troops retreated and riot police faced off with the protesters, who used metal sheets as barricades.

Men in civilian clothes standing on the roof of a building threw stones at protesters, who fired fireworks back.

Outrage flared on Sunday as furious protesters brandished the front page of a local paper showing military police clubbing a veiled woman after having ripped her clothes to reveal her bra.

In the picture and YouTube footage of the incident, the woman is sprawled on the ground, helmeted troops towering over her. One is seen kicking her, and later she appears unconscious, her stomach bared and her bra showing.

Other pictures circulating on social media networks that have enraged protesters include one of a military policeman looming over a sobbing elderly woman with his truncheon.

More footage showed army troops beating two protesters, a man and woman, before leaving their motionless bodies on the ground.

Field Marshal Hussein Tantawi, who heads the ruling military council, visited some of the wounded in hospital, state television showed.

The clashes were the deadliest in weeks and have sparked a furious debate over the army's role during the transition.

Some argue that the protesters are sabotaging the elections, seen by some as the first step to democratic rule.

But much remains unclear about how the new parliament will function and how much power it will be given by Supreme Council of Armed Forces (SCAF), headed by Mubarak's former defence minister Tantawi.

The health ministry said late Saturday that 10 people had been killed and at least 500 wounded since Friday.

The clashes also left the Institute of Egypt in flames.

The centre for the advancement of scientific research was founded in 1798 during Napoleon Bonaparte's expedition to Egypt, and contained more than 20,000 precious documents and manuscripts.

On Sunday, a group entered the premises to recover the manuscripts, some of which were burned, AFP correspondents said.

"We are trying to save whatever we can of these historic documents. The building can collapse any minute," said Olfa, with a bag of partly burned papers.

Culture Minister Shaker Abdel Hamid called the fire "a catastrophe for science."

"The building contained important manuscripts and rare books which have no parallel in the world," Abdel Hamid said on state television late Saturday.

The authorities have blamed the protesters for the deadly unrest.

The military council late on Saturday posted footage on its Facebook page and on YouTube of protesters ransacking a government office on Friday.

"Is it not our right to protect the people's property?" said a brief message.

Prime Minister Kamal al-Ganzuri raised tensions on Saturday by accusing the protesters of being counter-revolutionaries and denying security forces had opened fire on them.

"Those who are in Tahrir Square are not the youth of the revolution," he told a news conference.

"This is not a revolution, but a counter-revolution," added Ganzuri, who also served as premier under Mubarak.

His appointment last month by the SCAF, which has ruled since Mubarak's ouster in February, had prompted protesters to launch a sit-in outside the cabinet offices.

The demonstrators want the SCAF to hand over full powers to a civilian administration.

The military has said it will step down only once a president has been elected by the end of June in the final stage of a protracted transition.

The clashes pushed stocks down 3.46 percent on Sunday, with the main EGX-30 index plummeting to 3,782.74 points, the lowest since Mubarak was toppled.

The violence has also overshadowed the count in the second round of a three-stage parliamentary election which has seen Islamists emerge as the front-runners.

More than 40 people were killed in similar clashes between protesters and security forces just before the election's first round in November.

In another development, an explosion hit a gas pipeline to Israel and Jordan in the 10th such attack this year.

The blast south of the town of El-Arish in the north of the Sinai Peninsula targeted a segment of pipeline which was gas-free as it was under repair.