Boko Haram Islamists raided two towns in northeastern Nigeria, torching public buildings and looting food and fuel stores, residents and a police officer told AFP on Sunday.

Islamist gunmen in pick-up trucks and on motorcycles stormed the towns of Galda and Fika in Yobe state late Saturday, firing wildly and forcing residents indoors.‎

A suicide bomber killed at least nine people on Saturday inside a mosque in northeast Nigeria's city of Maiduguri, with the blast leaving much of the building destroyed, witnesses said.

"It was suicide attack by a bomber who pretended to be worshiper," said Haruna Dawud, a trader at the Monday Market which is next to the mosque.

Nigeria's military on Saturday repelled a Boko Haram attack on the key northeastern city of Maiduguri, a day after President Muhammadu Buhari took office vowing to crush the group, witnesses and security sources said.

The overnight attack on the Borno state capital saw rocket-propelled grenades fired into homes in a bombardment that reportedly lasted several hours.

Almost 40 countries pledged Friday to do more to protect students caught up in conflicts, including Nigeria and Afghanistan both of which have suffered armed attacks on schools in recent years.

"Targeted attacks on education are robbing a generation of the chance to realize their potential, with a huge long-term social cost," said Diya Nijhowne, director of the Global Coalition to Protect Education from Attack (GCPEA).

Muhammadu Buhari was sworn in as Nigeria's new president on Friday, vowing to tackle the country's many problems "head on", including Boko Haram, at a ceremony rich with military pomp and cultural tradition.

A 21-gun salute rang out across the capital, Abuja, after he took the oath of office before the chief justice of Nigeria to begin a four-year term beset with difficulties from the outset.

Two bombs exploded at a wedding venue in northeast Nigeria on Friday, killing seven and injuring dozens more, a witness and security sources said.

Witnesses said the blasts happened at about 6:00 am (0500 GMT) in the Tashan Alade area of Borno state, when families and friends of the bride and groom gathered to witness the ceremony.

The United Nations voiced fears Thursday that rescued women and girls who became pregnant in Boko Haram captivity will face stigmatization in conservative Nigerian communities, and that their babies could become "untouchable."

"For those of them who have (become) pregnant as a result of rape, what are the options available to them?" asked Munir Safieldin, U.N. deputy humanitarian coordinator in Nigeria.

A Spanish High Court judge said Thursday he has agreed to hear a lawsuit against Nigerian Islamist militant group Boko Haram and its leader Abubakar Shekau for crimes against humanity and terrorism.

Judge Fernando Andreu ruled he was competent to handle the case under the principle of universal jurisdiction -- which allows courts to try certain atrocities committed in other countries -- because the case concerns a Spanish nun who is a victim of the group.

A fundraising campaign to help Cameroon's army battle Nigeria's feared Boko Haram fighters has brought in more than three million euros and hundreds of tonnes of food, local media said Wednesday.

"2.1 billion CFA francs (3.2 million euros) already" collected to help troops fighting the Islamist group on Cameroon's northern border with Nigeria, said the national CRTV radio and TV network.

Niger has extended for three months the state of emergency in its southeastern Diffa region where the army has been battling Boko Haram militants since February, authorities announced Wednesday.

"Boko Haram elements are there," Daouda Malam Marthe, first vice president of parliament, said on state radio. "The prolongation of the state of emergency is a necessity."