VATICAN CITY — Pope Benedict XVI warned Sunday that terrorism, nihilism and "fanatic fundamentalism" threatened world peace, and he called on individuals, governments and institutions to work together to combat them.

Benedict made the appeal during a Mass in St. Peter's Basilica to mark New Year's Day, which the Roman Catholic Church celebrates annually as its World Day of Peace.

In his homily, the pope said a "shock" of courage and faith in God was necessary to spread peace, and that everyone must work together to combat the threats to it.

"It becomes ever more important to work together for peace when confronting the situations of injustice and violence that continue to oppress various parts of the world, those that are the new and most insidious threats to peace: terrorism, nihilism and fanatic fundamentalism," he said.

He said individuals, international organizations and world powers must take responsibility for promoting justice, solidarity and peace.

In particular, he called for the United Nations to assume a renewed understanding of its responsibility to promote peace and justice "in a world ever more marked by the vast phenomenon of globalization."

After the Mass, tens of thousands of people standing under a carpet of umbrellas to guard against a downpour jammed the piazza to hear Benedict issue New Year's Day greetings in a half-dozen languages from his apartment window.

Ambassadors accredited to the Vatican were among the hundreds of people who packed St. Peter's for the morning Mass, which also was celebrated by the pope's top diplomat, Cardinal Angelo Sodano, his deputies and Cardinal Renato Martino, who heads the Vatican's office for justice and peace.

During the Mass, youngsters dressed as the three kings and adults dressed in traditional costumes brought the offertory gifts up to the altar, which was decked with pines and flowers for the Christmas holiday season. Prayers were read out in a host of languages, including Chinese, Russian and Arabic.

The pope said he was praying that 2006 would "be for all of us a year of prosperity and peace."

The Mass came hours after Benedict presided over a New Year's Eve vespers' service in the basilica, which he capped with a brief visit to pray before the larger-than-life Nativity scene in St. Peter's Square.

Benedict's busy holiday schedule continues this week with his weekly general audience Wednesday, a Mass to mark Epiphany on Friday and a ceremony on Sunday in which he will baptize several newborns in the frescoed Sistine Chapel.

The baptism ceremony was a beloved tradition of Pope John Paul II, who often had to interrupt his prayers because the babies were crying. John Paul stopped performing the baptisms when he became too infirm.

The Vatican, meanwhile, issued Benedict's calendar of events for the next several months, confirming that he will follow in many of John Paul's footsteps as he marks the upcoming liturgical year.

On March 1, for example, he is scheduled to travel across town to a fifth-century basilica to mark Ash Wednesday, the start of the church's solemn Lenten season.

During Easter week in April, he is to celebrate Holy Thursday Mass at Rome's St. John Lateran basilica and then preside over the Way of the Cross commemoration of Christ's death April 14 during a torch-lit ceremony at Rome's Colosseum.

John Paul used to celebrate these rituals until he became unable to and others had to preside for him.

On April 3, a day after the first anniversary of John Paul's death, Benedict will preside over a special Mass in St. Peter's to commemorate the passing.