|Coptic Christians burned a car during clashes with police and Muslims following the church bombing [EPA]
At least 21 people have been killed in a New Year's day car bomb attack on a church in Alexandria.
The blast early on Saturday targeted Egypt's Christian community, the biggest in the Middle East.
After the explosion, enraged Christians emerging from the church clashed with police and stormed a nearby mosque, prompting fights and volleys of stone throwing with Muslims - a sign of the sectarian anger that has been arising with greater frequency in Egypt.
There was no immediate claim of responsibility for the attack, which came as nearly 1,000 faithful left the Al-Qiddissine church in the Sidi Bechr district of the northern city.
The interior ministry said in a statement that eight of those wounded were Muslims, and that the church and a nearby mosque were severely damaged.
According to the ministry, the car that exploded was parked in front of the church.
A witness told private television channel On-TV that he had seen a green Skoda car pull up outside the church shortly after midnight. Men got out and the explosion took place almost immediately after.
Police and troops then deployed en masse around the scene of the explosion as ambulances rushed to the area.
Refaa al-Tahtawi, spokesman for Al-Azhar, Sunni Islam's main institution based in Cairo, appeared on television to denounce the attack, which he said targeted "Egyptian national unity".
He also appealed to Christians and Muslims for calm.
Pope Benedict XVI on Saturday urged world leaders to defend Christians against injustice.
In the wake of mounting tensions and "especially discrimination, abuse and religious intolerance which are today striking Christians in particular, I once again launch a pressing appeal not to give in to discouragement and resignation," he said.
Al Jazeera's Ayman Mohyeldin, reporting from Cairo, said that the car bomb likely involved sophisticated remote-control timer technology.
"Churches in Egypt are heavily guarded, so undoubtedly questions will arise about how a car was parked so close to the church and who was able to detonate from a distance," he said.
While it was not known who was responsible for the blast, a group calling itself Al-Qaeda in Iraq had threatened the Egypt's Coptic Christian community.
Alexandria governor Adel Labib immediately blamed al-Qaida.
The bombing comes almost two months to the day after an October 31 attack by militants on Our Lady of Salvation church in central Baghdad, which left the 44 worshippers, two priests and seven security forces members dead.
Al-Qaeda's Iraqi affiliate claimed responsibility for that attack and made new threats against Christians.
The group threatened to attack Egyptian Copts if their church did not free two Christians it said had been "imprisoned in their monasteries" for having converted to Islam.
The two women were Camilia Chehata and Wafa Constantine, the wives of Coptic priests whose claimed conversion caused a stir in Egypt.
Protection around Copt places of worship was discreetly stepped up after the threats, as President Hosni Mubarak said he was committed to protecting the Christians "faced with the forces of terrorism and extremism".
The Copts, the biggest Christian community in the Middle East and who account for up to 10 per cent of Egypt's 80m population, often complain of discrimination and have been the target of sectarian attacks.
In 2006 a man attacked worshippers in three churches in Alexandria, killing one person and wounding others.
Authorities said at the time he had "psychiatric problems" but this was rejected by the Coptic community.
Clashes broke out between Copts and Muslims the following day at the funeral of the victim, with one person killed and several wounded.
In November clashes took place in a southwestern neighbourhood of Cairo between Copt demonstrators and police after local authorities refused to allow a community centre to be transformed into a church. Two Christians died and dozens were wounded.