Suspected ethnic Fulani herders killed at least 15 villagers and burnt down homes in Taraba state in eastern Nigeria in a dispute over grazing rights, police said on Wednesday.

State police spokesman Kwaji Joseph told AFP the incident happened on Sunday when the herdsmen stormed Dori and Mesuma in the Gashaka local government area.

Nearly 350 dead bodies were buried in a mass grave in northern Nigeria after clashes between the army and supporters of a Shiite cleric, a public official has told an inquiry into the unrest.

The testimony of Muhammad Namadi Musa, the director-general of the Kaduna State Interfaith Bureau, lends weight to claims that at least 300 people were killed in the violence in December last year.

Pirates have attacked a Turkish cargo ship off the coast of Nigeria, kidnapping six crew members in a region increasingly hit by piracy in recent years, the Nigerian navy said on Monday.

"All the six Turkish crew members, including the captain of the vessel, the chief officer and the chief engineer, were abducted by the attackers," Nigerian Navy spokesman Chris Ezekobe told AFP.

A female suicide bomber set off her explosives and the other was killed by troops outside the northeastern Nigerian town of Maiduguri, where a twin suicide attack last week killed 25 people, vigilantes said.

The two were spotted by civilian vigilantes helping the military fight the Boko Haram Islamist group at Molai around 1:00 am, vigilante Babakura Kolo told AFP.

Four people were killed in political violence that has forced the cancellation of election re-runs in the southern Nigerian state of Rivers, police and the Independent National Electoral Commission (INEC) said Monday.

Police said four people were killed and 22 arrests were made at the weekend for disrupting the electoral process, which INEC said included the barricading of its offices.

Some 20,000 people have been killed in the Boko Haram insurgency in Borno state in northeast Nigeria, according to a report for the World Bank that puts the cost of destruction at $5.9 billion.

The report lays bare the extent of the damage since the insurgency began in 2009 and which at one point saw the Islamists control swathes of territory across the northeast.

Nigeria's military on Thursday said suspected pirates killed two soldiers in a gun battle in the oil-producing south, where tensions are high before a re-run of disputed elections.

The shooting happened at about 11 am (1000 GMT) as troops in a speedboat were patrolling the creeks in Abonnema, west of the Rivers state capital, Port Harcourt.

At least 22 people were killed in a twin suicide bombing at a mosque in northeast Nigeria Wednesday, prompting condemnation from President Muhammadu Buhari and stoking fresh fears about security.

The attack, carried out by two women disguised as men, took place at about 5:30 am (0430 GMT) in the Molai district of Maiduguri, which Boko Haram insurgents have repeatedly targeted in the past.

Three civilian vigilantes on their way to fight Boko Haram in northeast Nigeria were killed and seven others injured when their vehicle hit a landmine, residents told AFP on Tuesday.

The vigilantes from Chul village in Borno state were moving on Monday evening to battle Boko Haram militants who had stormed the neighboring village of Huyum when the accident occurred.

The International Organization for Migration flew 172 Nigerian migrants including six women home from Libya on Friday, the organization said.

An AFP cameraman said a child was among the migrants who left Tripoli's Mitiga airport at 4:30 am (0230 GMT) dressed in tracksuits and sports shoes.