Clashes erupted between protesters and police in Cairo and two other Egyptian cities, killing two people and wounding hundreds in the biggest security challenge yet for the country's ruling generals days before scheduled elections.

In scenes reminiscent of the 18-day uprising that toppled Hosni Mubarak from three decades of power in February, hundreds of youths chanted, The people want to topple the regime, as they rushed toward riot police, who fired rubber bullets and tear gas.

Protesters broke chunks of cement from pavements and hurled them at police in clashes in which police lost control of Cairo's landmark Tahrir Square twice during the day.

A blaze broke out around midnight at the huge Mogamma state administration building overlooking Tahrir.

As police fired round after round of tear gas at protesters near the interior ministry, protesters closer to Tahrir laid sheets of metal to block roads into the square.

They unleashed 20 trucks to forcefully disperse a few dozen peaceful protesters this morning, Salah Saeed said as he handed out vinegar-doused napkins to protect protesters against the tear gas.

Now thousands of Egyptians are protesting in Tahrir. We don't need the corrupt interior ministry or the military council, he said.

Staggered voting is due to begin Nov. 28, but it could be disrupted if violence spreads.

The vote is being overshadowed by a row between political parties and the government over ground rules for a draft constitution that could leave the army free of civilian control.

The army won popular backing during Mubarak's overthrow for maintaining order and pledging to hand power to an elected government, but support has ebbed over its use of military trials for civilians and suspicion that it wants to continue to wield the levers of power after a new government is sworn in.

A security official said on Saturday police had used lawful methods to deal with troublemakers. Protesters said they were incensed by brutal police tactics to break up a peaceful sit-in.

State news agency MENA quoted the health ministry's spokesman as saying 676 people had been hurt in Cairo and that Ahmed Mahmoud, a 23-year-old demonstrator, died in a hospital. MENA reported another death in Egypt's second-largest city, Alexandria.

The army stayed away from the fighting.

I tell you do not leave the square. This square will lead the way from now on, presidential candidate Hazem Salah Abu Ismail, a hard-line Islamist, told a group of protesters early on Sunday. Tomorrow the whole of Egypt will follow your lead.

Unrest in Alexandria and Suez, Too

About 5,000 protesters had converged on Tahrir on Saturday afternoon when police tried to evict the remnants of a 50,000-strong demonstration a day earlier, mostly by Islamists demanding the departure of the military.

Buildings and two cars in the square were set on fire, witnesses said. A third vehicle close to the Arab League's headquarters was also burned.

Police beat the protesters, most of whom were not Islamists, with batons and fired tear gas to regain control of Tahrir, only to retreat after night fell.

Protests erupted in other cities, as well. About 800 people gathered in front of the security directorate in Alexandria and chanted, Interior Ministry officials are thugs.

A witness heard repeated gunfire in the area. It was not clear whether the shots were live bullets. One person covered in blood was carried off to hospital on a motorcycle.

About 1,000 gathered outside a police station in the eastern city of Suez, threw stones at it, and tried to force their way in. Police fired tear gas and shot into the air.

Protesters in Suez tore down banners of former members of Mubarak's disbanded party who are running in the election.

Liberal groups are dismayed by the military trials of thousands of civilians and the army's failure to scrap a hated emergency law.

Islamists eyeing a strong showing in the next parliament suspect the army council wants to curtail their influence and is maneuvering to stay in power from behind the scenes.

Muslim Brotherhood

Analysts say Islamists could win 40 percent of parliament seats, with a big portion going to the Muslim Brotherhood.

The demonstrators denounced Field Marshal Mohamed Hussein Tantawi, head of the ruling military council, and some criticized the Muslim Brotherhood, which they accused of working to further its own political ends.

We are not political parties, and we hate the Brotherhood who gave up on the revolution and the people, Medhat Fawzy said. We are Egyptian youth, he added, flashing victory signs.

Egyptian state television said Prime Minister Essam Sharaf had called on protesters in Tahrir to clear the square.

The television outlet said 40 of the wounded were police officers and that 18 troublemakers had been arrested.

The liberal April 6 Youth movement said the interior minister should quit for ordering the use of force against a peaceful protest.

Friday's rally appeared to be the biggest Islamist challenge to military rule since the largely secular uprising that toppled Mubarak. The demonstrators were mostly Brotherhood members and their harder-line Salafi rivals.

Protesters expressed anger at a draft constitution that Deputy Prime Minister Ali al-Silmi showed to political groups this month that would give the army exclusive authority over its internal affairs and budget.

Al-Silmi and the Brotherhood appeared to be negotiating, through press statements and the state news agency, on percentages of members of parliament needed to approve the committee that would write the constitution.

MENA reported that al-Silmi had amended some clauses of the constitutional proposal, including one to say Egypt was a democratic state instead of democratic civil state, a move likely to anger liberals who fear that a parliamentary majority could seek to turn Egypt into an Islamic state.

Al-Silmi said the committee chosen to write the constitution would not be confined to the larger groups in parliament so as to ensure a constitution that reflects national consensus and receives the consent of all segments of society.

Political analyst Ezzedine Fishere said he did not expect the amendments to appease Islamist groups.

What is happening now is a showdown between the two factions ... an on-the-ground confrontation with each party trying to enforce its will, the military council from one end and the Islamist currents from the other, said Fishere.

(Additional reporting by Omar Fahmy, Patrick Werr, Tamim Elyan, Abdel Rahman Youssef and Yousri Mohamed; Editing by Tom Pfeiffer and Ralph Gowling)