CAIRO – Egyptian troops blasted protesters with water cannons, tear gas and live ammunition, trying to prevent them from marching on the Defense 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 Defense Ministry, which has emerged as a flashpoint for the protesters´ anger after nine 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 epicenter 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 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 Defense 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.

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 at least 373 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.

The Committee to Protect Journalists said Friday that at least 18 journalists have been assaulted, injured, or arrested in the past three days while covering Cairo clashes. CPJ also called on the ruling military to "identify the attackers and bring them to justice immediately, as well as to release journalists in custody."

Maj. Gen. Mukhtar al-Mullah, a member of the military council, warned late Friday in a televised statement that those involved in or instigating violence would be arrested. The daily Al-Ahram quoted an unidentified military official as saying 50 men who were allegedly hiding inside a mosque with automatic weapons were among those arrested.

Violence also spread the port city of Suez where anti-military protesters pelted the building of the governor´s office with stones. Seven were arrested.

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 Defense Ministry and said soldiers have the right to defend their positions.

Friday´s clashes centered around the pro-Abu Ismail sit-in that has been maintained for a week in a square several blocks away from the heavily guarded Defense Ministry. The Salafis have been involved in past fighting but for the first time were in the front lines, signaling a dangerous escalation in tensions.

The more politically savvy Brotherhood called for the march to Abbasiyah on Thursday but stayed in Tahrir on Friday. Some liberal and leftist groups joined the Salafis in Abbasiyah on Friday to show solidarity after Wednesday´s deaths but most of them later withdrew.

"The farce in Abbasiyah showed that this is a battle that does not serve any interest for the Egyptian people," said the leftist group April 6. "We decided to withdraw and not participate in the shedding of Egyptian blood."

Others accused Abu Ismail of dragging the country to confrontation with the military, reflecting divisions over whether to support the Salafis who oppose the military but also are known to include Islamic extremists.

"The man has believed his own lies and is now land-mining Egypt to serve his own interests," wrote Ibrahim Eissa, a chief editor of the independent Tahrir daily.

The circumstances surrounding the deadly clashes on Wednesday that launched the current round of tensions remain unclear as protesters at the sit-in and Abbasiyah residents traded allegations.

Protesters said that the assailants were hired thugs or plainclothes police and troops, similar to past attacks. They also said the military allowed Wednesday´s attack to take place, noting troops nearby did nothing to stop fighting for hours.

But residents and activists said some of the protesters were armed and provoked the situation.

Alaa Abdel-Fatah, a prominent democracy activist, claimed in several tweets that protesters had weapons.

"The revolutionaries also fired live ammunition in the middle of residential streets," he tweeted on Wednesday. "We have battled with the wrong people, and we have threatened innocent souls secure in their houses." (© 2012 The Associated Press 05/04/12)