The United States said it was worried by violence in Egypt and urged the army rulers to respect human rights as security forces wielding batons and firing teargas fought for a fourth day on Monday with protesters demanding an end to military rule.

U.N. Secretary-General Ban Ki-moon also condemned excessive use of force by security forces in Cairo protests that 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.

Police and soldiers using batons drove stone-throwing protesters out of Cairo's Tahrir Square, hub of the uprising that ousted Hosni Mubarak in February, during the night but by dawn they had trickled back into the square. Security forces took up positions again behind barricades in nearby streets.

Protesters, who hurled rocks at police, had fled down sidestreets, away from sensitive areas where parliament, the cabinet offices and Interior Ministry are located. Security forces used teargas in nearby streets to drive protesters away.

The violence broke out just after the second stage of a six-week election for Egypt's new parliament that starts the slow countdown to the army's return to barracks. The military has pledged to hand power to an elected president by July.

U.S. Secretary of State Hillary Clinton said she was deeply concerned about the violence and urged the security forces to respect and protect the universal rights of all Egyptians.

In a statement to a nation which has received billions of dollars in U.S. military and other aid, she also called on protesters to refrain from acts of violence.

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 that have killed 10 people and wounded hundreds.

Soldiers in riot gear have been filmed beating protesters with batons even after they have fallen to the ground. A Reuters picture showed two policemen dragging a woman lying on the street by the shirt, exposing her underwear.

Protesters said they had seized four soldiers who had been part of formations who launched a charge in the early hours.

We quickly got the four into vehicles and drove them away from the square, otherwise they would have been beaten to a pulp by angry protesters who experienced the army's vicious attacks, said Sayyid Abu Ella, speaking by telephone from Tahrir.

Late on Sunday, protesters had hurled petrol bombs at lines of security forces and chanted Down with Tantawi a reference to Field Marshal Mohamed Hussein Tantawi who heads the army council and was Mubarak's defence minister.

OVERSHADOWING ELECTIONS

Ban Ki-moon is 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 U.N. Secretary-General's office said in a statement.

The violence has overshadowed a staggered parliamentary election that is set to give Islamists the biggest bloc.

The West, which long looked to strongmen in the region like Mubarak to keep a lid on Islamists, have watched warily as Islamist parties swept elections in Morocco, Tunisia and now Egypt.

A hard core of activists have camped in Tahrir since a protest against army rule on November 18 that was sparked by the army-backed cabinet's proposals to permanently shield the military from civilian oversight in the new constitution.

Tough police and army tactics combined with hot-headed youths bent on keeping up pressure also sparked a flare-up last month that killed 42 people.

A small group of activists approached protesters hurling stones on Sunday and called on them to stop, but they refused, citing the deaths of 10 people as a reason not to negotiate.

Other activists handed over to the army people they said were making petrol bombs.

The violence has deepened the frustration of many ordinary Egyptians, who want an end to 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, adding the army should have managed the transition better.

The Health Ministry said on Sunday that 10 people had been killed in the violence since Friday and 505 injured, of whom 384 had been taken to hospital.

The latest bloodshed began after the second round of voting last week for parliament's lower house. The staggered election began on November 28 and will end with a run-off vote on January 11.

The Muslim Brotherhood and other Islamist parties repressed in the 30-year Mubarak era have emerged as strong front-runners.

(Additional reporting by JoAnne Allen in Washington, John O'Callaghan, Tamim Elyan, Shaimaa Fayed and Reuters Television; Writing by Edmund Blair; Editing by Tim Pearce)