Clashes between Muslims and Coptic Christians in a Cairo suburb left 12 people dead, dozens wounded and a church charred in one of the most serious outbreaks of violence Egypt’s interim rulers have faced since taking power in February.

The unrest began Saturday night in the Imbaba district northwest of Cairo, as a mob of hard-line Muslims attacked the Virgin Mary church. A separate group of youths also attacked an apartment building several blocks away, residents said.

The assaults were the latest agitation triggered by allegations that Copts have held women against their will because they intended to convert to Islam.

Clashes also broke out Sunday during demonstrations attended by Copts and Muslims to show unity and demand better protection from the government. As tension escalated, security forces cordoned off several parts of the city Sunday afternoon to quell the violence.

The increase in religious violence appeared to catch Egypt’s military rulers by surprise. They have struggled with continued unrest after a popular uprising that ousted President Hosni Mubarak on Feb. 11.

Salafists, a faction of ultraconservative Muslims, have become increasingly visible in recent months. Christians accuse Salafists of seeking to boost their standing ahead of elections, scheduled for this fall, by fomenting religious tension.

Demonstrators gathered outside Tahrir Square and outside the building that houses the main Egyptian television station. Witnesses said it was difficult to determine the motive for the violence that broke out during the Sunday demonstrations.

“A lot of rocks and bottles were being thrown under the bridge, but I noticed that there were no Salafi types” around, said Sharif Kouddous, a freelance journalist who was present. “It was hard to tell who was throwing, but there were lots of thugs.”

Tension between Muslims and Copts, who make up roughly 10 percent of Egypt’s population of about 80 million, is not new. But in recent months, as Egyptians have become emboldened to air their grievances publicly, confrontations between members of the two communities have become increasingly common.

Youssef Sidhom, the editor of the Coptic newspaper al-Watani, said the rumors of women being held for converting to Islam appear to be a ploy by a small group of Salafists.

“They want to assert themselves in the political arena, and their means to do so is to highlight rumors of conversion cases of ladies,” Sidhom said Sunday. “That is their way of creating a buzz.”

He said Copts feel that security forces stood by as the worst of the violence unfolded Saturday in Imbaba, a poor district. “From Saturday afternoon, there were signs that this was going on,” Sidhom said. “The police were alerted, but they did nothing to stop this.”

Michael Mounir, a Christian activist, said Salafists are trying to present themselves as an alternative to the secular military leaders. The generals were appointed by Mubarak, who led a secular government.

“The Salafists have managed to show that the army is weak and that the army is unable to distinguish between democracy and freedom of opinion and thuggery,” Mounir said. “This is clearly thuggery.”

On Sunday, Prime Minister Essam Sharaf canceled a trip to the Persian Gulf to preside over an emergency cabinet meeting, state television reported.

The Justice Ministry and the military rulers issued separate statements calling for swift punishment for the perpetrators. The statements, however, were at odds on a key matter. The military said the 190 people detained by authorities would face military tribunals. The Justice Ministry said the aggressors would be prosecuted in regular courts.

The Justice Ministry’s statement warned that authorities would strictly implement laws “governing thuggery and demonstrations that threaten security.”

The controversy over the conversions began two years ago when a woman married to a Coptic priest was reported to be having marital problems. Muslim leaders charged that Copts were holding her against her will because she was attempting to convert to Islam — an allegation Copts have denied.

The woman, Camilla Shehata, gave an interview televised Saturday in which she said she remained a Christian and disputed that she had attempted to convert to Islam.

After the interview aired, Coptic leaders said, Muslims in Imbaba began to assert that Christians were holding a second woman hostage to prevent her from converting to Islam.

The original controversy and others like it were cited as the motive in the Oct. 31 attack on a Syriac Catholic church in Baghdad that killed more than 51 people. Tensions also were heightened after a New Year’s Eve bombing outside a church in the Egyptian coastal city of Alexandria that killed more than 20 people.

Special correspondent Sherine Bayoumi contributed to this report.