Thousands of police clashed with protesters for control of downtown Cairo's Tahrir Square on Saturday after security forces tried to stop activists from staging a long-term sit-in there, killing one man and injuring more than 600 people.

Health officials say a 23-year-old man died in hospital from a bullet wound and at least 676 people have been injured.

The violence took place just nine days before Egypt's first elections since the ouster of President Hosni Mubarak in February.

In scenes reminiscent of the 18-day uprising, protesters and police forces hurled rocks at each other, and crowds swarmed an armoured police truck, rocking it and setting it ablaze. Black smoke rose over the crowd.

Witnesses said the violence began when riot police dismantled a small tent camp set up to commemorate protesters killed in the uprising and attacked around 200 peaceful demonstrators who had camped out in the square overnight.

Tens of thousands of people had gathered in Tahrir Square on Friday to denounce Egypt's ruling military council, which has been heavily criticized for its oversight of Egypt's bumpy transition period. Protesters are angry with attempts by the military to give themselves special powers over a future elected government.

'Violence breeds violence'

Military officials are trying to change the constitutional guidelines, giving the military and its budget protection from civilian oversight. An early version of it also said the military would appoint 80 members of the 100-person constitutional committee — a move that would vastly diminish the new parliament's role.

Back in February, the military had promised it would return to the country to civilian rule within six months. Now, there is deep uncertainty over the timeline, and presidential elections might not be held until 2013.

'We are tired of this and we are not leaving the square.'—Sahar Abdel-Mohsen

Anger over the military's manoevres erupted on Saturday a Tahrir Square with police firing rubber bullets, tear gas and beating protesters with batons to clear the area, said Sahar Abdel-Mohsen, an engineer who joined in the protest after a call went out on Twitter telling people to come down to Tahrir.

Abdel-Mohsen said a friend was wounded by a rubber bullet that struck his head and that she saw another protester wounded by a pellet shot in his neck.

"Violence breeds violence," Abdel-Mohsen said. "We are tired of this and we are not leaving the square."

Saturday's confrontation was one of the few since the uprising to involve police forces, which have largely stayed in the background while the military takes charge of security. There was no military presence in and around the square on Saturday.

The black-clad police were a hated symbol of Mubarak's regime.

Protesters say they heard police officials telling their officers to aim their rubber bullets at heads. Reuters

Ghada Shahbandar, a member of the Egyptian Organization for Human Rights, said her colleague, Malek Mostafa lost his right eye from a rubber bullet.

"I heard an officer ordering his soldiers to aim for the head," said Shahbandar.

Protesters ran from police into surrounding side streets only to charge back into the square. Protests continued into the evening.

The number of protesters swelled to several thousand as news of the scuffles spread in the city, and thousands more riot police streamed into Tahrir Square, blocking entrances and clashing with protesters.

Crowds chanted: "Riot police are thugs and thieves" and "Down with the Marshal," referring to Field Marshal Hussein Tantawi, Egypt's military ruler.

12,000 tried in military courts

While the military tolerates daytime demonstrations in the central square — a symbol of the country's Jan. 25-Feb. 11 uprising — it claims long-term occupation paralyzes the city.

Activist Mona Seif said Saturday's attacks on protesters were unwarranted.

"This violence is the same as the old regime," Seif said. "Police are telling us they are carrying out orders to beat us until we leave."

Seif is the sister of prominent blogger and activist Alaa Abdel-Fattah, who is in jail after refusing to answer questions over his alleged role in sectarian clashes. He leads a campaign to end the trials of civilians in military courts.

Rights groups estimate that up to 12,000 people have been tried in military courts since Mubarak was ousted.