Pope Francis presided at two Good Friday services, praying for persecuted Christians a day after Islamist militants attacked a university in Kenya, killing at least 147 people.

Modern-day religious persecution was the common thread in both of the pope's appearances on the day Christians around the world commemorate Jesus' crucifixion.

"We see in you (Jesus) our persecuted brothers, beheaded and crucified because of their faith in you, before our eyes or often with our complicit silence," Francis said after a traditional Via Crucis (Way of the Cross) procession at Rome's ancient Colosseum.

The pope spoke in a somber voice after people from Italy, Iraq, Syria, Nigeria, Egypt, China, the Middle East and Latin America took turns carrying a wooden cross between the 14 "stations" commemorating the last hours of Jesus' life.

In their attack on the university in Kenya on Thursday, Al Shabaab militants initially killed indiscriminately but later freed some Muslims and targeted Christian students during a siege that lasted about 15 hours..

At another Good Friday service earlier in St. Peter's Basilica, Francis heard the Vatican's official preacher accuse the international community of indifference to the persecution of Christians today.

Father Raniero Cantalamessa, whose title is "preacher of pontifical household," mentioned the Kenya attack at a long "Passion of the Lord" service, during which the pope prostrated in prayer on the marble floor of St. Peter's Basilica.

That service is one of the few times he listens while someone else preaches.

"Christians are, of course, not the only victims of homicidal violence in the world, but we cannot ignore that in many countries they are the most frequently targeted victims," Cantalamessa said.

Cantalamessa denounced "the disturbing indifference of world institutions and public opinion in the face of all this killing of Christians ..."

Cantalamessa also mentioned the beheading of 22 Egyptian Coptic Christians last February by Islamic State militants in Libya.

Francis has expressed alarm over the plight of Christians targeted for their faith and has said the international community would be justified in using military force as a last resort to stop "unjust aggression" by Islamic State.

Good Friday was the second of four consecutive days of papal activities culminating on Easter Sunday.

On Saturday night, the leader of the world's 1.2 billion Roman Catholics celebrates an Easter Eve service in St. Peter's Basilica. On Sunday, he delivers his twice yearly "Urbi et Orbi" (to the city and the world) blessing and message.