Pope Benedict XVI condemned religious intolerance, especially against Christians, in a New Year's appeal Saturday that came hours after a bomb blast outside an Egyptian church killed 21 people as worshippers left Mass.

The pope urged Christians in his homily at St. Peter's Basilica to remain strong in the face of discrimination and intolerance, echoing comments last month in which he called a lack of religious freedom a threat to world security.

"In the face of the threatening tensions of the moment, especially in the face of discrimination, of abuse of power and religious intolerance that today particularly strikes Christians, I again direct a pressing invitation not to give in to dismay and resignation," he said.

The Catholic church dedicates New Year's Day to world peace and the pope urged world leaders to make a "concrete and constant commitment" to help.

"I exhort everyone to pray so that the efforts made by many sides to promote and build peace in the world achieve a good end," the pope said.

Benedict has repeatedly denounced a violent campaign against Christians in Iraq blamed on al-Qaida militants, including an October attack on a Baghdad Catholic church that claimed 68 lives, including those of two priests.

The Vatican is very worried that an exodus of minority Christians from Iraq will permanently reduce their numbers and discourage the wider, ancient community of Christians in the Middle East.

On Saturday, a bomb exploded in front of a Coptic Christian church in the Egyptian city of Alexandria, killing at least 21 people in an attack that raised suspicions of an al-Qaida role.