CAIRO (AFP) -- President Hosni Mubarak urged Egypt's Christians and Muslims to unite and confront "terrorism" after a New Year's day car bomb killed 21 people at a Coptic church in Alexandria, in the latest blow to the Middle East's largest Christian community.
There was no immediate claim, but Al-Qaeda has threatened Christians everywhere, and called for punishment of Egypt's Copts, over claims that two priests' wives they say had converted to Islam were being held by the church against their will.
The health ministry's Abderrahman Shahine said 21 people were killed and 43 wounded.
The car, which was parked outside the Al-Qiddissine (The Saints) church in the Sidi Bechr district of the Mediterranean port city, exploded at around half past midnight (2230 GMT Friday) as worshippers were leaving after a service.
A witness told private television channel On-TV he had seen a green Skoda pull up outside the church shortly after midnight. Two men got out and the explosion occurred almost immediately afterwards.
The interior ministry said eight of those wounded were Muslims, as there was a mosque nearby.
"If the bishop had finished saying mass two minutes earlier, the bloodbath would have been worse," Nermin Nabil, who suffered a leg injury in the attack, said from her hospital bed.
The 30-year-old mother told AFP she had left the church "just two minutes before the bishop finished mass. Hundreds of people were still inside."
Saturday morning dozens of Christians were protesting outside the church.
"Where is the government," they shouted.
A security services source said dozens of angry Christians also demonstrated outside the mosque, whose door and windows were damaged by the blast.
Police and troops deployed en masse around the scene as ambulances rushed to the area.
In a country suffering from growing sectarian tensions, Mubarak urged Christians and Muslims to close ranks and confront "terrorism."
He called on the "children of Egypt -- Copts and Muslims -- to close ranks and confront the forces of terrorism and those who want to undermine the security, stability and unity of the children of this nation," state news agency MENA said.
Refaa al-Tahtawi, spokesman for Al-Azhar, Sunni Islam's Cairo-based main institution of learning, denounced the attack, which he said targeted "Egyptian national unity."
He also appealed for calm.
While it was not immediately known who was responsible, the attack came two months after gunmen stormed a Baghdad cathedral and took the worshippers hostage.
In a raid to free them, 44 worshippers, two priests and seven security forces were killed.
The attack was claimed by Al-Qaeda affiliate, the Islamic State of Iraq, which said its purpose was to force the release of the two women in Egypt.
"All Christian centres, organisations and institutions, leaders and followers, are legitimate targets for the mujahedeen (holy warriors) wherever they can reach them," the group said.
"Let these idolaters, and at their forefront, the hallucinating tyrant of the Vatican, know that the killing sword will not be lifted from the necks of their followers until they declare their innocence from what the dog of the Egyptian Church is doing," the ISI said.
It also demanded that the Christians "show to the mujahedeen their seriousness to pressure this belligerent church to release the captive women from the prisons of their monasteries."
The Alexandria attack came just two days after more anti-Christian violence in Baghdad, when a series of bombings killed two Christians and wounded 16.
Protection around Copt places of worship was discreetly stepped up after the threats, as Mubarak said he was committed to protecting the Christians "faced with the forces of terrorism and extremism".
The Copts account for up to 10 percent of Egypt's 80-million population, and often complain of discrimination and have been the target of sectarian attacks.
Saturday's bombing came almost a year after gunmen killed six Copts as they emerged from Christmas liturgy in a town in southern Egypt. Three Muslim men were accused of the murders and a verdict in their case is expected on January 16.
Sectarian tensions have been rising since November, when Muslims set fire to homes owned by the family of a Christian man rumoured to have flirted with a Muslim girl.
Also in November bloody clashes erupted in Cairo between Coptic protesters and police over the refusal of local authorities to allow them to turn a community centre into a church.
Copts are required to obtain a presidential decree to construct new religious buildings and must satisfy numerous conditions before permission is granted.
In November, a US State Department report complained about the state of religious freedom in Egypt, singling out minority groups such as Christians, saying they "face personal and collective discrimination."