ALEXANDRIA, Egypt -- Thousands of police manned barricades around Christian churches in Egypt's second largest city Saturday, a day after Muslim rioters attacked churches and shops, leaving four people dead in the country's worst religious violence in five years.

Egypt's top Muslim and Christian leaders appealed for calm as tensions simmered in Alexandria, where some 5,000 Muslim rioters rampaged through two predominantly Christian neighborhoods.

Clashes with rubber bullet-firing police killed two rioters and two policemen, police and hospital officials said Saturday. At least 90 people were injured.

The violence followed a week of protests over the distribution of a DVD of a play deemed offensive to Muslims. St. George's Coptic Church, where the play was performed two years ago, was one of the seven churches attacked Friday.

The play, entitled "I Was Blind But Now I Can See," tells the story of a young Christian who converts to Islam and becomes disillusioned.

Islamic leaders accused Copts of releasing the DVDs and demanded an apology.

But political leaders and security officials said Islamic extremists distributed the DVDs in an effort to tarnish a Coptic Christian candidate running in next month's parliamentary elections for Alexandria's impoverished Ghorbal constituency.

Maher Khalah, one of two Copts running on the ruling National Democratic Party ticket in this mainly Sunni Muslim country, announced Saturday that he was withdrawing from the race to prevent any recurrence of the violence.

"This violence is not about the DVD, it is all about the elections," Khalah told The Associated Press.

Coptic Christians, who account for about 10 percent of Egypt's population of 72 million, complain of discrimination but generally live in harmony with the Muslim majority. Violence flares occasionally, particularly in small southern communities.

Friday's violence was the bloodiest since January 2000, when an argument between a Coptic shopkeeper and a Muslim customer swelled into gunfights and other street battles that killed 23 people, mostly Christians, in el-Kusheh, a town south of Cairo.

In a joint statement, the head of the Coptic Orthodox Church, Pope Shenouda III, and Egypt's highest Islamic authority, Grand Sheik of al-Azhar Mohammed Sayyed Tantawi, urged Christians and Muslims not to resort to violence.

"We call on everyone to be calm so we can spread the grace of peace, security and affection among us," the religious leaders said. "If something happened and was misunderstood, then it is our duty to deal with it in the spirit of dialogue and understanding."

Shenouda canceled a trip to Alexandria on Saturday for his annual Ramadan fast-breaking meal with Muslim officials because of the violence, church leaders said.

Coptic community leader Kamil Sediq warned that the repercussions of Friday's violence could spread to Cairo and other provinces and reiterated that the church would not apologize.

"We're not going to apologize because we don't want it to become a precedent," said Sediq, of the Coptic Community Council, a secular body of prominent Copts established in 1874 to oversee affairs of the community. "We did nothing to apologize for."