A young female suicide bomber killed 12 worshipers when she blew herself up in a mosque in northeastern Nigeria, a witness and a vigilante aiding the military against Boko Haram said Friday.

"The bomber was a girl aged around 15 who was seen around the mosque when worshipers were preparing for the afternoon prayers," vigilante Danlami Ajaokuta said of Thursday's attack in Malari village, adding 12 had died and seven were injured.

Suspected Boko Haram militants killed nearly 150 people in northeastern Nigerian villages, mowing down men and children while they prayed in mosques and shooting women preparing food at home, witnesses said Thursday.

Dozens of militants stormed three remote villages in the flashpoint Borno state on Wednesday evening, slaughtering residents and setting houses ablaze in the bloodiest day of attacks by the extremist group since President Muhammadu Buhari came to power in May.

A man and a woman apparently trying to target a hospital in northeast Nigeria were killed Wednesday when explosives strapped to their bodies blew up, witnesses said.

The explosions took place in the village of Molai not far from the restive city of Maiduguri, capital of Borno state, where Vice-President Yemi Osinbajo was on a surprise visit.

The United Nations rights chief on Wednesday urged Nigeria to show compassion and make it easier for women and girls who became pregnant in Boko Haram captivity to access abortions.

Boko Haram militants are estimated by Amnesty International to have kidnapped more than 2,000 women and girls in northeastern Nigeria since the beginning of 2014, including the 276 girls seized from their school in Chibok last year in a kidnapping that sparked global outrage.

Five Chadian police officers and six Islamists were killed Monday when suspected Boko Haram militants blew themselves up during a police raid on a safe house in the capital N'Djamena, the interior minister said.

The blasts struck after security forces arrested the alleged "brain" behind Boko Haram operations in Chad and neighboring northern Cameroon, Interior Minister Abderahim Bireme Hamid said.

At least five people have been killed and 10 wounded after a suicide bomber blew himself up outside a leprosy hospital on the outskirts of the northeast Nigerian city of Maiduguri, emergency services said.

The bomber, who tried to gain access to the hospital, detonated his explosives outside the building at around 5:30 pm (1630 GMT) on Saturday.

U.S. President Barack Obama will welcome his Nigerian counterpart to Washington next month, the White House announced Thursday, a symbolic show of solidarity after the country's first ever democratic transition.

"President Obama will host Nigerian President Muhammadu Buhari at the White House," on July 20, the White House said.

Two Lebanese men have been kidnapped by armed men in Nigeria's oil-producing south, local media reported on Thursday.

Two policemen were also killed during the kidnapping operation at Bayelsa State in the Niger Delta, said the reports.

Suspected Boko Haram gunmen shot dead at least 42 people in two separate attacks in northeast Nigeria, with no let-up in sight to the Islamist group's targeting of civilians.

The attacks in the remote villages of Debiro Hawul and Debiro Biu in Borno state on Monday and Tuesday came before at least 10 people were killed in a suicide attack in neighboring Yobe.

A girl thought to be aged just 12 detonated explosives she was carrying at a market in northeast Nigeria on Tuesday, killing 10 people and injuring dozens, a relative of one of the injured told Agence France Presse.

The blast bore all the hallmarks of Boko Haram Islamists, who have used young women and girls in the past as human bombs and regularly attacked "soft" civilian targets such as markets.