CAIRO >> Relations between Egypt’s Muslims and Christians degenerated to a new low Sunday after riots overnight left 12 people dead and a church burned, adding to the disorder of the country’s post-revolution transition to democracy.

The attack on the church was the latest sign of assertiveness by an extreme, ultraconservative movement of Muslims known as Salafis, whose increasing hostility toward Egypt’s Coptic Christians over the past few months has met with little interference from the country’s military rulers.

Salafis have been blamed for other recent attacks on Christians and others they don’t approve of. In one attack, a Christian man had an ear cut off for renting an apartment to a Muslim woman suspected of involvement in prostitution.

The latest violence, which erupted in fresh clashes Sunday between Muslims and Christians who pelted each other with stones in another part of Cairo, also pointed to the weakness of the armed forces council that has taken temporary control of the country after Hosni Mubarak’s Feb. 11 ouster from the presidency.

After the overnight clashes in the slum of Imbaba, residents turned their anger toward the military. Some said they and the police did almost nothing to intervene in the five-hour frenzy of violence.

The bloodshed began Saturday around sundown when word spread around the neighborhood that a Christian woman who married a Muslim had been abducted and was being kept in the Virgin Mary Church against her will.

The report, which was never confirmed by local religious figures, sent a large mob of Muslims toward the church. Christians created a human barricade around the building and clashes erupted. Gunfire sounded across the neighborhood, and witnesses said people on rooftops nearby were firing into the crowd.

The two sides accused each other’s camp of firing first.

Crowds of hundreds of Muslims from the neighborhood lobbed firebombs at homes, shops and the church. Residents say Christians were hiding inside. Muslims chanted: "With our blood and soul, we defend you, Islam."

Rimon Girgis, a 24-year-old with a tattoo of a Coptic saint on his arm, was among the Christians who formed a human shield around the church.

"They were around 40 bearded men chanting slogans like "There is no God but Allah." After rallying Muslim residents, they opened fire," he said. "We Copts have to respond so we hurled stones and pieces of broken marble."

Some of the wounded were carried to the nearby St. Menas Church, where floors were still stained with blood hours later.

"Every five minutes, an injured person was rushed into the church," said a Father Arshedis. "We couldn’t reach ambulances by phone. We called and no one answered. We tried to treat the injured. We used the girls’ hair clips to extract the bullets."

"The army is responsible because they take no action," he said.

Later the same night, the Muslim crowd moved to a Christian-owned apartment building nearby and set it on fire.

Some soldiers and police did fire tear gas, but failed to clear the streets for hours.

By daybreak, the military had deployed armored vehicles and dozens of troop carriers to cordon off a main street leading to the area. They halted traffic and turned away pedestrians. Men, women and children watching from balconies took photos with mobile phones and cheered the troops.

Across the Nile river, in downtown Cairo, more clashes broke out on Sunday afternoon. Muslim youths attacked Coptic Christian protesters, said Christian activist Bishoy Tamri.

TV images showed both sides furiously throwing stones, including one Christian who held a large wooden cross in one hand while flinging rocks with another.

Scores were injured, but an army unit securing the TV building did nothing to stop the violence, Tamri said.

Islamic clerics denounced the violence, sounding alarm bells at the escalating tension during the transitional period following Mubarak’s Feb. 11 ouster by a popular uprising.

"These events do not benefit either Muslim or Copts," Ahmed al-Tayyeb, the sheik of al-Azhar, told the daily Al-Ahram.

Sameh Fawzi, a Coptic scholar, said the new trend of attacks on churches and heightened tension between ultraconservative Muslims and Copts are taking place in the context of a weakened state and increasingly assertive Salafis.

The military rulers’ attempts to hold reconciliation sessions, instead of prosecuting those involved, only serves to reinforce the impression of the state’s weakness, he said.

"What needs to happen and quickly is that the state implements the law," he said. "This is a crime of thuggery and it should be treated as such."

During the 18-day uprising that ousted Mubarak, there was a rare spirit of brotherhood between Muslims and Christians. Each group protected the other during prayer sessions in Cairo’s Tahrir Square, the epicenter of the revolution.

But in the months that followed, there has been a sharp rise in sectarian tensions, as the once quiescent Salafis have become more forceful in trying to spread their version of an Islamic way of life. In particular, they have focused their wrath on Egypt’s Christians, who make up 10 percent of the country’s 80 million people.

On Friday, a few hundred Salafis marched through Cairo to celebrate al-Qaida leader Osama bin Laden and condemning the U.S. operation that killed him.

Critics say Egyptian military authorities have done too little to stem the religious violence. But authorities arrested 190 people after the church attack, sending them to military prosecutions and threatening the maximum penalty against anyone attacking houses of worship.

Copts complain of widespread discrimination, including tight strictures on building or repairing churches that do not exist for Muslim places of worship.

In one of the worst attacks against them, a suicide bomber killed 21 people outside a church in the port city of Alexandria on Jan. 1, setting off days of protests. Egypt made some arrests but never charged anyone with the attack.

Tensions have been building for the past year as Salafis protested the alleged abduction by the Coptic Church of a priest’s wife, Camilla Shehata. The Salafis claim she converted to Islam to escape an unhappy marriage — a phenomenon they maintain is common.

Because divorce is banned under the Coptic Church, with rare exceptions such as conversion, some Christian women resort to conversion to Islam or another Christian denomination to get out of a marriage.

Shehata’s case was even used by Iraq’s branch of al-Qaida as a justification for an attack on a Baghdad church that killed 68 people and other threats by the group against Christians.

On Saturday just before the violence erupted in Imbaba, Shehata appeared with her husband and child on a Christian TV station broadcast from outside of Egypt and asserted that she was still a Christian and had never converted.

"Let the protesters leave the Church alone and turn their attention to Egypt’s future," she said from an undisclosed location.