Clashes Sunday in Nigeria's restive northeast killed five Boko Haram Islamists and 13 fighters from a vigilante group which has fought a series of recent battles with the Islamists, a state government official said.

Members of the civilian militia heard that Islamists were planning to attack the town of Benishiek in Borno state, Boko Haram's historic stronghold, said Garba Ngamdu, an aide to the state governor.

Gunmen suspected to be Boko Haram Islamists stormed the northeast Nigerian town of Gajiran on Thursday, opening fire in a market and killing 15 people, residents said.

Borno state in the northeast, Boko Haram's stronghold where the latest violence occurred, has seen a spate of similar attacks on locals in recent weeks.

At least 38 people have been killed in two weekend attacks in Nigeria blamed on Boko Haram insurgents, local government officials said Saturday.

Armed men killed 14 nomadic herders after invading their village, and 24 members of a vigilante group were killed in a separate incident, local officials in the north eastern state of Borno said.

Two attacks by suspected Boko Haram insurgents have killed 24 people in Nigeria's northeast in the latest violence believed to be in revenge against vigilantes, residents and officials said Tuesday.

A survivor and a hospital source spoke of 18 people killed in the town of Bama on Sunday. A resident and a military source said six people were killed in Damasak on Monday.

Gunmen killed four policemen who attempted to prevent the abduction of a prominent lawyer on a road in southern Nigeria, police said Sunday.

The Edo state police said in a statement that one of its units responded to an emergency call warning that armed men were active on a road near Benin City, east of Lagos, on Saturday.

Thousands of Muslims rallied peacefully in northern Nigeria on Saturday to demand the return of Egypt's Islamist former president Mohammed Morsi, ousted by the military early last month.

Around 4,000 demonstrators carrying banners and placards chanted pro-Morsi songs and slogans outside a mosque in northern Nigeria's biggest city, Kano, an Agence France Presse reporter witnessed. Organizers put the number of protesters at 5,000.

Islamist insurgents dressed as soldiers opened fire on worshipers leaving a mosque in Nigeria's far northeast this week, killing at least 35 in the second such attack this month, officials said on Friday.

"Boko Haram people attacked the village on the ground that they have refused to cooperate with them, that they refused their message," defense spokesman Brigadier General Chris Olukolade told Agence France Presse of the incident in Dumba, referring to Islamist extremist group Boko Haram.

Doubts persisted on Tuesday over a Nigerian military claim that the leader of Islamist extremist group Boko Haram may have been killed, with questions raised over the timing of the announcement.

A security task force in northeastern Nigeria issued a statement on Monday saying Abubakar Shekau, declared a "global terrorist" by the United States, "may have died" from a gunshot wound after a clash with soldiers on June 30.

Nigeria's army said Monday that the leader of Islamist extremist group Boko Haram, branded a "global terrorist" by the United States, may have died following a clash with soldiers.

Intelligence reports "available to the (military) revealed that Abubakar Shekau, the most dreaded and wanted Boko Haram terrorists leader, may have died," a statement said.

Four Thais and a Nigerian held in an apparent ransom kidnapping in southern Nigeria have been freed unharmed, officials in both countries said Saturday.

"The four of them were released at exactly 2:00 am (0100 GMT) this morning," the agricultural commissioner in Nigeria's Rivers state, Emmanuel Chindah, told AFP.