Christians sparred with riot police in the Egyptian city of Alexandria after a suspected suicide bombing outside a church killed at least 21 people, in the worst violence against the country's Christian minority since the late 1990s.

The bomb exploded in front of the Saints Church about a half hour after midnight early Saturday, as nearly 1,000 worshippers were leaving a New Year's Mass.

Ninety-seven people were wounded, according to Health Ministry spokesman Abdel-Rahman Shahine. It's not known if all the victims were Christians.

"The last thing I heard was a powerful explosion and then my ears went deaf," Marco Boutros, a 17-year-old survivor, told the Associated Press from his hospital bed. "All I could see were body parts scattered all over -- legs and bits of flesh."

It's unclear where the blast originated. Police initially said the bomb came from a an explosives-packed car outside the church, but later reports showed little sign of a crater that large car bombs usually cause.

An Interior Ministry statement on the official news agency said: "It is likely that the device which exploded was carried by a suicide bomber who died among others."

The circumstances of the attack "clearly indicates that foreign elements undertook planning and execution," the statement added. Most recent anti-Christian violence has involved shootings and stabbings; Saturday's attack was clearly more planned and sophisticated.

President Hosni Mubarak said the bombing "carries evidence of the involvement of foreign fingers" and vowed to pursue the perpetrators.

The attack was the deadliest against Christians in a decade and comes after repeated threats by al Qaeda militants in Iraq to attack Egypt's Christians. There was no immediate claim of responsibility.

The government in Cairo has insisted for years that al Qaeda does not have a large presence in the country. If that terror network was involved in the attack, it could mean that Egypt faces another serious security threat.

The country has witnessed growing tensions in recent years between its Muslim majority and Christian minority, made up mostly of Orthodox Copts. The Christians say they face discrimination at the hands of Muslims and accuse the government of covering up attacks on their community.

Saturday's bombing prompted new violence from crowds of young Christian men, who hurled stones at riot police in the streets outside the church and a neighbouring hospital. Police responded by firing rubber bullets and tear gas.

"Now it's between Christians and the government, not between Muslims and Christians," one Christian woman hollered.

Mubarak promised in a televised address that terrorists would not divide Christians and Muslims in Egypt. He said the bombing was an attack against "all Egypt" and that "terrorism does not distinguish between Copt and Muslim."

Archbishop Arweis, the top Coptic cleric in Alexandria, said police want to blame a suicide bomber so they can write it off as a lone attacker. He denounced what he called a lack of protection.

"There were only three soldiers and an officer in front of the church. Why did they have so little security at such a sensitive time when there's so many threats coming from al Qaeda?" he told the Associated Press.

The attack was the deadliest involving Christians in Egypt since 1999, when clashes killed at least 20 people in a southern town.

With reports from the Associated Press