More than 5,000 Catholics have been killed by Boko Haram in a single Nigerian diocese, a new report has revealed.

According to the 'Situation Report on the activities of Boko Haram in the Catholic Diocese of Maiduguri', up to 85 per cent of the diocese, in the north-east of Nigeria, is currently controlled by Boko Haram. The Islamist group began its insurgency in 2009, and has been largely active in Borno, Yobe and Adamawa states, all of which fall within the Maiduguri constituency.

The report states that at least 100,000 Catholics in the area have been displaced, and more than 350 churches have been attacked. Some 7,000 women in the diocese are now widowed, and nearly 10,000 children orphaned by the violence, which has spread to neighbouring Chad, Cameroon and Niger.

Obtained by Aid to the Church in Need (ACN), the report also reveals that over half of the diocese's 40 parish centres and chaplaincy centres have been abandoned by the faithful, and several are now occupied by Boko Haram militants. Four of five convents have also been closed.

"People are very scared and those who are able to return home find there is nothing left," Father Gideon Obasogie, director of social communications in the diocese, told ACN.

"A life lived with much fear is terrible."

However, the Catholic priest said his faith was being strengthened in the midst of adversity. "The good Lord has always been on our side. He has seen us through thick and thin. Our faith has been purified through persecution."

National security became the central talking point of Nigeria's presidential election in March, after the date was postponed by six weeks while the government tried to curb Boko Haram's insurgency. President-elect Muhammadu Buhari is due to take office later this month and has promised to tackle the ongoing problem.

Boko Haram would "soon know the strength of our collective will," Buhari vowed in a televised speech.

"In tackling the insurgency, we have a tough and urgent job to do. Boko Haram will soon know the strength of our collective will. We should spare no effort until we defeat terrorism."

On Monday, Buhari met Chadian President Idriss Deby to discuss a combined effort to restore stability to the region.

"If we want to continue the fight we'll have to make sure that our two armies work together. This is the only way that we can get results," Deby said, according to the BBC.

"We discussed issues of common interest which we will pursue together and to have a joint action to handle the issue of Boko Haram and will overcome it and by the grace of God, peace and security will prevail in the sub-region."