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Khalil Hamra, Associated Press
An Egyptian Coptic Christian woman holds a cross and chants angry slogans as she protests the recent attacks on Christians and churches, in front of the state television building in Cairo, Egypt, Sunday, May 9, 2011. A security official says authorities have detained 23 people in connection with recent clashes between Muslims and Christians, including two people suspected of sparking riots over the weekend that left a Cairo church torched and 12 people dead.

CAIRO — Hundreds of Egyptians protested violence against the country's Coptic Christian minority Monday after Muslim mobs burned a church and sparked riots in Cairo that left 13 people dead.

Spiraling sectarian tension is emerging as a major fault line in the tumultuous aftermath of the popular uprising that forced Hosni Mubarak from power in February. Protesters criticized the interim military rulers for their handling of the weekend violence and demanded the officer in charge of the country resign.

Demonstrators, who numbered about 1,000 by midday, said they feared that some in Egypt seek to replace Mubarak's three decades of autocratic rule with an Islamic state that would marginalize Christians, who make up about 10 percent of Egypt's nearly 80 million people. Most are Coptic Christians.

Some of the protesters gathered outside the headquarters of state-run TV along the Nile. Some stones were thrown toward the building, but the protest was largely peaceful.

"We don't want to bury our heads in the sand," said Rami Kamel, a Coptic protester. "The issue is bigger than rebuilding a church or arresting the culprits. This is Egypt's fate. Is Egypt becoming a religious state or can we change course and opt for a civil state?"

Authorities arrested 23 more people on Monday, including two accused of sparking the riots, which started late Saturday and marked a new low in Muslim-Christian relations in Egypt.

Some of the Christian protesters outside the state TV building demanded that measures be taken to control a movement of ultraconservative Muslims known as Salafis that has grown more assertive after the fall of Mubarak. Residents of the Cairo neighborhood where the rioting took place say Salafis orchestrated the violence.

The riots were sparked by a rumor that a Christian woman married to a Muslim man had been abducted by church officials and was being held there against her will.

Muslim mobs attacked two churches in the Imbaba neighborhood, burning one. One more person died Monday of injuries from the clashes, bringing the death toll to 13. More than 200 people were injured. The unrest continued Sunday afternoon, when Muslims and Christians pelted each other with stones in another part of Cairo.

Fifteen Egyptian rights groups warned of a "civil war" in the absence of decisive measures to enforce law and order.

"The new wave of sectarian violence threatens to turn Egypt into a battlefield of civil war between Muslims and Christians," the groups said in a statement. The groups accused the military rulers of not taking decisive measures and of turning a blind eye to the "incitement of religious hatred and sectarian violence" in return for political compromises.

Police and soldiers moved in to break up the weekend violence, but it was hours before they effectively cleared the streets around the churches in Imbaba. Authorities arrested 190 people immediately after the church attack, sending them to military prosecutions and threatening the maximum penalty against anyone attacking houses of worship.

In another recent episode of tension, tens of thousands of Egyptians led by Islamists believed to be affiliated with the Salafis demonstrated last month to protest the appointment of a Coptic Christian governor in southern Egypt.

In an attempt to mend relations, Egyptian activists marched in a street rally in Imbaba on Monday, chanting "Long live Egypt" and waving Egyptian flags and banners with the crescent and the cross together.

Wael Ghonim, a former Google executive in Egypt who was one of the organizers of the Jan. 25 protests that started the 18-day uprising against Mubarak and his regime, addressed the rally along with a Coptic priest.

"A Muslim and a Christian are one hand," Ghonim said, borrowing a slogan of unity from the revolution.

Residents chanted, "The people want national unity."

Among those arrested Monday was Yassin Thabet, 31, a Muslim who claimed his Christian wife was being held against her will in the church in Imbaba. Authorities also detained the owner of a cafe opposite the church from where witnesses said gunfire had originated.