Pope Francis has written to Nigerian bishops, condemning "new and violent forms of extremism" that are plaguing the country, and urging them to continue to promote peace and reconciliation.

The letter, which was released by Vatican yesterday but dated March 2, acknowledges Nigeria's significant role in global politics. "At the same time," Francis writes, "your nation has had to confront considerable problems, among them new and violent forms of extremism and fundamentalism on ethnic, social and religious grounds."

"Many Nigerians have been killed, wounded or mutilated, kidnapped and deprived of everything: their loved ones, their land, their means of subsistence, their dignity and their rights. Many have not been able to return to their homes."

Both Christians and Muslims have experiences the same plight, Francis adds. Each at the hands of people "who claim to be religious, but who instead abuse religion, to make of it an ideology for their own distorted interests of exploitation and murder."

The letter does not mention Boko Haram by name, but comes no doubt in response to the group's insurgency, primarily focussed in the north of the country. The same week in which the letter was sent, Boko Haram pledged allegiance to Islamic State in Iraq and Syria and called upon Muslims all over the world to do the same. The leader of ISIS later accepted the allegiance, and his spokesman urged those who could not travel to the Middle East to enter combat in Africa instead. Boko Haram's pledge opened a "new door for you to migrate to the land of Islam and fight," Abu Mohammad al-Adnani said.

Francis says that he prays for the Nigerian church every day, and says that while peace is a gift from God, it is also a "daily endeavour".

"[It is a] courageous and authentic effort to favour reconciliation, to promote experiences of sharing, to extend bridges of dialogue, to serve the weakest and the excluded. In a word, peace consists in building up a "culture of encounter"," he writes.

"And so I wish here to express my heartfelt thanks to you, because in the midst of so many trials and sufferings the Church in Nigeria does not cease to witness to hospitality, mercy and forgiveness. How can we fail to remember the priests, religious men and women, missionaries and catechists who, despite untold sacrifices, never abandoned their flock, but remained at their service as good and faithful heralds of the Gospel?

"To them, most particularly, I would like to express my solidarity, and to say: do not grow tired of doing what is right!"

Francis ends his letter by urging the bishops not to become discouraged, but to "go forward on the way of peace".

"Accompany the victims! Come to the aid of the poor! Teach the youth! Become promoters of a more just and fraternal society!" he writes.

"May the Resurrection of the Lord bring conversion, reconciliation and peace to all the people of Nigeria!"