Egyptian troops blasted protesters with water cannons, tear gas and live ammunition, trying to prevent them from marching on the Defence Ministry Friday in clashes that left one soldier dead and scores of people injured just three weeks ahead of presidential elections.

The fierce street battles raised fears of a new cycle of violence surrounding the upcoming vote to replace Hosni Mubarak, who was ousted more than a year ago. For the first time in Egypt's chaotic transition, hard-line Islamists, rather than secular forces, were at the forefront of the confrontation with the military rulers who have been accused of trying to cling to power.

The military council imposed an 11 p.m. to 7 a.m. curfew on the area surrounding the Defence Ministry, which has emerged as a flashpoint for the protesters' anger after 11 people were killed on Wednesday in clashes between unidentified assailants and protesters who mainly comprised supporters of a disqualified Islamist presidential candidate.

The violence has thrown the campaign for the May 23-24 elections into turmoil, with two front-runners and several other candidates temporarily suspending their campaigns to protest the military's handling of the situation.

Thousands of demonstrators massed in Cairo's downtown Tahrir Square — the epicentre of last year's popular uprising — earlier Friday for what has become a weekly rally to demand that the generals speed up a transition to civilian rule.

Protesters cut through barbed wire

Protesters included the powerful Muslim Brotherhood and ultraconservative Islamists known as Salafis but also revolutionary youth who spearheaded the mass rallies that ousted Mubarak.

Despite official warnings against gathering, groups marched to the district of Abbasiyah to join a sit-in outside the Defence Ministry initially held by supporters of Hazem Abu Ismail. A lawyer-turned-preacher, hard-line Abu Ismail was disqualified from the race because his late mother allegedly held dual Egyptian-American citizenship, making him ineligible under election laws. He has encouraged his followers to take to the streets.

"We are in the face of a plot to abort the revolution," his spokesman Gamal Saber told the Al-Jazeera network on Friday. Violence appeared to have ensued when protesters tried to cut through barbed wire barricading them from troops blocking access to the road that leads up to the ministry. Some protesters chanted "peaceful, peaceful" to deter fighting, but the clashes began after troops fired water cannons at protesters and hurled stones to keep them from advancing.

The protesters took shelter behind metal sheets snatched from a nearby construction site and hurled back stones. Others climbed the roof of a nearby university and showered soldiers with rocks from above. The troops then opened up with heavy volleys of tear gas that pushed the demonstrators back. Protesters sat fire to garbage to raise smoke to lessen the impact of the gas.

Troops snatched one protester and beat him with metal sticks, tearing his clothes and leaving his back bloody — a scene aired live on state TV. Soldiers with body shield and red helmets also were seen carrying a soldier who collapsed with his nose bleeding.

296 injured, officials say

After several hours, troops swept through the protesters' camp, set tents on fire and drove them out of the area. Armored vehicles cordoned off several streets and occupied the main square and surrounding areas, including a big mosque. At least two subway stations were closed and military helicopters were seen circling the site of clashes.

The Health Ministry said one soldier was killed and 296 people were injured.

More than 170 were arrested by the military, according to a security official, who spoke on condition of anonymity because he wasn't authorized to release the information. Several journalists, including a Belgian photographer, also were detained or injured as they were caught up in the chaos.

Anger at the ruling military council, which took power after Mubarak's ouster, has risen across the political spectrum as the generals are accused of steering a messy transition, using oppressive measures and maneuvering to maintain a degree of power even after the presidential election and handover of authority.

The Islamists have joined in after the disqualification of two heavyweight Islamists, Abu Ismail and Muslim Brotherhood chief strategist Khairat el-Shater, whose group has been frustrated that its domination of parliament — where it holds nearly half the seats — has not translated into political power.

The generals promised Thursday to hand over power after one of the 13 remaining candidates wins an outright victory, but they also warned against protests near the Defence Ministry and said soldiers have the right to defend their positions.