Egyptian police and soldiers using batons and teargas have fought opponents of army rule in Cairo for a fourth day, taking the death toll since Friday to 13, according to medical sources.
Hundreds more have been wounded and scores detained in attempts to disperse protests in and around Cairo's Tahrir Square, hub of the uprising that ousted Hosni Mubarak in February.
U.N. Secretary-General Ban Ki-moon condemned the use of excessive force against the protests, which have widened a rift among Egyptians over the role of the army and cast a shadow over the country's first free election in decades.
An army general told a news conference that evil forces wanted to sow chaos and said soldiers had shown self-restraint despite provocation by those trying to burn down buildings and create discord between the army and the people.
The human rights watchdog Amnesty International called on arms suppliers to stop sending small arms and ammunition to Egypt's military and security forces in the wake of the violent crackdown on protesters.
Reporters Without Borders said the army's systematic use of violence against media personnel, was blocking access to information in and around the square.
Soldiers have been filmed using batons to beat protesters, many of whom have been hurling stones, even after they have fallen to the ground.
In one incident, a government building housing historic books has been set on fire.
What is your feeling when you see Egypt and its history burn in front of you? retired general Abdel Moneim Kato, an adviser to the military, told a local paper, Al-Shorouk.
Yet you worry about a vagrant who should be burnt in Hitler's incinerators.
The latest round of violence broke out just after the second stage of a six-week election for Egypt's new parliament that starts a slow countdown to the army's return to barracks. The military has pledged to hand power to an elected president by July.
An army source said 164 people had been detained. A security source said a 26-year-old man had died in custody, although the cause of death was not immediately clear.
The state news agency MENA said the public prosecutor had detained 123 people accused of resisting the authorities, throwing rocks at the army and police, and setting fire to government buildings. The prosecutor had released 53 others.
From the start of the revolution, the evil forces have wanted to drag Egypt into chaos, putting the army into confrontation with the people, General Adel Emara said.
What is happening does not belong with the revolution and its pure youth, who never wanted to bring down this nation.
He said troops had faced people wielding knives, petrol bombs and other weapons, and that those guarding state buildings had a right to self-defence.
Many Egyptians want to focus on building democratic institutions, not street activism, but have nevertheless been shocked by the tactics of security forces in and around Tahrir.
Video footage showed two soldiers dragging a woman lying on the ground by her shirt, exposing her underwear, then clubbing and kicking her.
General Emara described it as an isolated incident that was being investigated. He also said the army had not given orders to clear Tahrir Square by force.
Ban Ki-moon's office said he was highly alarmed by the excessive use of force employed by the security forces against protesters, and calls for the transitional authorities to act with restraint and uphold human rights, including the right to peaceful protest.
The violence has overshadowed the election, which is set to give Islamists the biggest bloc in parliament.
Western powers, long friendly with Mubarak and other Arab strongmen who kept a lid on Islamists, have watched warily as Islamist parties have swept elections in Morocco, Tunisia and now Egypt following this year's Arab uprisings.
Hard-core activists have camped in Tahrir since a protest against army rule on November 18, which was sparked by the army-backed cabinet's proposals to permanently shield the military from civilian oversight in the new constitution.
Tough security tactics against angry youths also sparked a flare-up last month in which 42 people were killed.
Some activists asked protesters to stop hurling stones on Sunday, but they refused. Other activists handed over to the army people they said were making petrol bombs.
The violence has deepened the frustration of many Egyptians tired of months of unrest that has left the economy in tatters.
There are people who wait for any problem and seek to amplify it ... The clashes won't stop. There are street children who found shelter in Tahrir, said Ali el-Nubi, a postal worker.
(Additional reporting by JoAnne Allen in Washington, John O'Callaghan, Tamim Elyan, Shaimaa Fayed and Dina Zayed; Writing by Kevin Liffey; Editing by Michael Roddy)