Two female suicide bombers believed to have ties with the Boko Haram terrorist group blew themselves up in a Nigerian city last week, killing nine people, including a pastor who belonged to the Church of Christ in Nigeria, the persecution watchdog World Watch Monitor reported. Twenty-four others were injured in the twin explosions.

The first female suicide bomber reportedly blew herself up outside the Bakassi IDP camp, housing an estimated 16,000 people, killing five men.

Half an hour later, another female suicide bomber driving a taxi detonated the explosives inside the vehicle by hitting a fuel tanker "to cause maximum damage and casualty," according to a Nigerian military spokesman as reported by the BBC.

Prior to the bombings, new Boko Haram leader Abu Musab al-Barnawi declared that his group will now focus on attacking Christians.

Instead of targeting fellow Muslims at mosques and marketplaces, the terrorist group will now focus on attacking Christian humanitarian groups that allegedly "exploit the condition of those who are displaced under the raging war, providing them with food and shelter and then Christianising their children," according to World Watch Monitor.

In a statement, al-Barnawi vowed to "booby-trap and blow up every church that we are able to reach" and kill all "citizens of the cross."

Al-Barnawi took over the leadership of the Nigerian-based Islamist extremist group in August this year. He was previously the spokesman of the group.

He said Boko Haram "remained a force to be reckoned with" and that it had been drawing new recruits, all of whom had vowed to fight the "Christianisation of society."

Under al-Barnawi's leadership, the terrorist group has become more radical and carried out more killings. Boko Haram has also sworn allegiance to the Islamic State (ISIS), referring to itself as ISIS "West African province."

Al-Barnawi said that under his leadership, Boko Haram will work to regain territories it had lost 18 months ago.

The group is fighting to overthrow Nigeria's government. For the past seven years, it has killed more than 20,000 people and drove more than 2.5 million from their homes, reports said. From time to time it stages suicide bombings in northeast Nigeria and neighbouring Cameroon, Niger and Chad.

According to the 2015 Global Terrorism Index, Boko Haram was the world's deadliest terrorist group in 2014—responsible for the death of 6,644 people, compared to ISIS, which was responsible for 6,073 deaths.