Pope Benedict denounced violence against Christians on Saturday hours after a bomb killed 21 people in a church in Egypt in the latest in a string of attacks against Christians in the Middle East and Africa.
On the day the Catholic Church celebrates its World Day of Peace, the pope dedicated his New Year's Day homily to religious freedom and tolerance.
"Humanity ... cannot be allowed to become accustomed to discrimination, injustices and religious intolerance, which today strike Christians in a particular way," he said.
"Once again, I make a pressing appeal (to Christians in troubled areas) not to give in to discouragement and resignation," he said.
Hours earlier, in the northern Egyptian city of Alexandria, a bomb at a Coptic Christian church killed 21 people as worshippers gathered to mark the New Year, officials said.
About 79 people were wounded in the bombing, which prompted hundreds of Christians to take to the streets in protest. Some Christians and Muslims pelted each other with rocks, a witness said. Cars were torched.
The attack in Muslim-majority Egypt, where Christians make up about 10 percent of the nation's 79 million people, was the latest against Christians that has worried Church officials.
Last week on Christmas Day, six people died in attacks on two Christian churches in the northeast of Nigeria, Africa's most populous nation, and six people were injured by a bomb in a Roman Catholic Church on the island of Jolo in the Philippines.
In a message issued last month for today's peace day, the pope said Christians were the most persecuted religious group in the world today and that it was unacceptable that in some places they had to risk their lives to practise their faith.
In November, 52 hostages and police officers were killed when security forces raided a Baghdad church to free more than 100 Iraqi Catholics captured by al Qaeda-linked gunmen.
The Vatican fears that continuing attacks, combined with severe restrictions on Christians in countries such as Saudi Arabia, are fuelling a Christian exodus from the region.
In his New Year's homily before a congregation of some 10,000 in St Peter's Basilica, the pope said "words were not enough" to bring about peace, particularly in the Middle East.
He called for "concrete and constant commitment" from national leaders and said everyone on a local level should push for peace in their daily relations with their neighbours.