At least 21 people have been killed at a Egyptian church in an explosion officials have blamed on a suicide bomber with foreign links.
At least 70 others were injured in the attack, during a new year's service at the al-Qiddissin (Saints) Church in the northern port city of Alexandria, attended by about 1000 people, the BBC reports.
As the service drew to a close after midnight, a bomb went off in the street outside.
Officials initially thought the cause was a car bomb, but the interior ministry later ruled it out, saying the attack was instead "carried out by a suicide bomber who died among the crowd".
The device was packed with pieces of metal shrapnel to cause the maximum amount of harm, a statement said.
Coptic Christians and Muslims clashed after the attack, but police moved in and used tear gas to restore order.
President Hosni Mubarak urged Egyptians to unite against "terrorism". In a televised statement, he blamed "foreign hands" for the bombing.
"Wicked terrorists targeted the nation, Copts and Muslims," he said. "It is a terrorist operation that is alien to us... We will all cut off the head of the snake, confront terrorism and defeat it."
No group has yet claimed responsibility for the attack.
Sectarian tensions have been increasing recently across Egypt, with violent incidents every couple of weeks.
Christians in Muslim-majority Egypt make up about 10% of the nation's 79 million people.
Egypt, due to hold a presidential election in September, had also stepped up security around churches, restricting cars from parking directly outside them, after an al Qaeda-linked group in Iraq issued a threat against the church in Egypt in November.