Video | Egypt church bombing investigation focuses on local group

The bombing sparked riots and protests by Egypt's Christian minority, who feel they are targeted and discriminated against and do not get adequate protection from authorities.

There were signs of heightened security outside churches nationwide and dozens returned to pray Sunday in the bombed, blood-spattered Saints’ Church — many of them sobbing, screaming in anger and slapping themselves in grief.

No group has so far claimed responsibility for the attack on Coptic Christians leaving a midnight Mass about a half hour into the New Year on Saturday - the worst attack on Egyptian Christians in a decade.

Reacting to the bombing, Egyptian President Hosni Mubarak blamed foreigners as Alexandria’s governor accused al-Qaida, pointing to threats against Christians by the terror network's branch in Iraq.

But security officials said police are currently looking at the possibility that home-grown Islamic extremists were behind the bombing, possibly inspired by al-Qaida though not directly under foreign command.

Investigators were also examining lists of air passengers who arrived recently in Egypt from Iraq, al-Qaida in Iraq threatened Christians in both countries. Any evidence of an al-Qaida financier or organizer who may have visited Egypt to recruit operatives is being sought.

Crime lab investigations have found that the explosives used were locally made and were filled with nails and ball bearings – anti-personnel configurations that attempt maximize the number of casualties. Investigators were also examining two heads found at the site on suspicion that at least one was the bomber's.

Security officials, speaking on condition of anonymity, confirmed that 25 people have been detained for questioning, but none of them were thought linked to the attack - mostly owners of cars parked outside the church at the time, storekeepers and Muslim neighbors known to be Islamic fundamentalists.

The attack was dramatically different from past violence against Christians, which included shootings but not serious bombings, much less suicide attacks. Christians, mainly Orthodox Copts, make up about 10 per cent of Egypt's mainly Muslim population of nearly 80 million.

The attack only served to heighten tensions that have been growing in recent years between Christians and Muslims. Those tensions were on display in the center of the capital Cairo on Sunday, where about 2,000 riot police were deployed outside the city's landmark TV and radio building as protesters marched nearby.

In Alexandria, about 500 Christians staged a noisy protest near the bombed church. Riot police outnumbered them by at least two to one and prevented them from moving elsewhere. Police arrested and beat up three demonstrators, according to witnesses.

Christians also staged demonstrations in at least three other cities.