Five police officers and three soldiers have been killed in separate attacks in Nigeria's oil-producing south, police and the army said on Wednesday.

The violence comes after increasing attacks against oil facilities by militants wanting a fairer share of revenue for local people in the delta region.

Amnesty International on Wednesday urged Nigeria to shut down a military detention facility for Boko Haram suspects after nearly 150 people, among them children and babies, died there in custody.

Militants have blown an offshore oil facility operated by U.S. oil group Chevron in southern Nigeria, the navy and the company said on Friday, in renewed violence that could hit exports in Africa's largest oil producer.

"There was an attack on a Chevron facility near Escravos on Wednesday night. The incident happened about four nautical miles from Escravos, near Warri, in Delta state," spokesman Chris Ezekobe told AFP.

Nigeria and France on Thursday signed an agreement on closer military cooperation, including intelligence sharing, to strengthen the fight against Boko Haram in the Lake Chad region.

Nigerian Defense Minister Mansur Dan Ali said the agreement was evidence of a "growing partnership" between Abuja and Paris, as he met his French counterpart Jean-Yves Le Drian in the capital.

Niger's government has extended a state of emergency in southeastern territory for three months because of the deadly danger from Boko Haram Islamists based in neighboring Nigeria, state television reported Thursday.

"The security situation in the Diffa region remains alarming because of the high level of threat due to attacks by Boko Haram," said a cabinet statement read on state television.

Six Turkish sailors kidnapped early this month from aboard their vessel off the coast of Nigeria have been released unhurt, a maritime consultancy firm said on Tuesday.

Pirates attacked the merchant tanker used for crude oil operations on April 11 while it was steaming through the oil-rich Niger Delta and seized the sailors, including the captain.

Suspected Boko Haram gunmen on horseback killed at least 11 people in northeast Nigeria this week, two civilian vigilantes assisting the military told AFP on Thursday.

The attack on Zango village, in the Gulani district some 150 kilometers (94 miles) south of the Yobo state capital, Damaturu, happened overnight on Tuesday to Wednesday, said Aisami Mamman.

A northeast Nigerian state, the worst hit in the country by the Boko Haram insurgency, needs greater international assistance for rebuilding as it faces funding issues and a food crisis, its governor said on Tuesday.

Borno state governor Kashim Shettima said "we need the whole world to rally round us" to help peace-building, rehabilitation and reconstruction after nearly seven years of violence.

Boko Haram fighters attacked Nigerian troops early on Monday, the army said, after two suspected suicide bombers were shot dead near military positions.

Army spokesman Sani Usman said in a brief emailed statement: "Boko Haram terrorists attack troops of 113 Battalion at Kareto, northern Borno state.

Nigeria's security services have hailed the arrest of the leader of the Boko Haram splinter group Ansaru, Khalid al-Barnawi, saying it will lead to them to other senior Islamist commanders.

"The arrest of Barnawi is a huge success and will have a profound effect on counter-terrorism operations in Nigeria and beyond," one security source told AFP.