Three secondary school students who were kidnapped from their school in Nigeria's biggest city, Lagos, have been found, police told AFP on Sunday.

"We have rescued the three girls in the early hours of today (Sunday)... in Igbokuta village," said Lagos State police spokeswoman Dolapo Badmus.

More than 100 people were arrested in Nigeria's commercial capital, Lagos, after bloody riots in the city's biggest food market left at least three people dead, police said on Friday.

"The police have arrested 105 suspects in connection with the disturbances in and around 'Mile 12' market," Lagos state police spokeswoman Dolapo Badmus told AFP referring to rioting which took place on Thursday.

Authorities in Nigeria's largest city have ordered security to be increased at schools after heavily armed gunmen abducted three girls, the state governor's spokesman told AFP on Thursday.

Unidentified gunmen seized the teenagers from their dormitory at the Babington Macaulay Junior Seminary School in Ikorodu, an eastern suburb of Lagos, late on Monday.

Turkish President Recep Tayyip Erdogan said Wednesday he was ready to help combat terrorism in Nigeria, where Boko Haram fighters have killed thousands of people in a bloody campaign for a hardline Islamic state.

He also signed a memorandum on trade and economic cooperation, which Nigerian President Muhammadu Buhari said was "just the beginning of what we have in the pipeline."

Nigerian police were on Wednesday hunting three girls who were abducted by armed men from their school on the outskirts of the country's biggest city, Lagos.

The abduction of students from school is rare in Lagos, Nigeria's sprawling megacity of 20 million people and the country's commercial hub.

Niger Delta oil rebels have freed five foreign hostages seized last month off the coast of Nigeria, a maritime consultancy firm and the Russian foreign ministry said on Thursday.

The Greek-flagged chemical tanker MT Leon Dias was hijacked on January 29 near Brass in the restive oil-rich region, in southern Nigeria.

Four people were killed when an improvised explosive device seized from Boko Haram Islamists detonated at a police station in northeast Nigeria, a rescue official said on Thursday.

"They were all police officers," the Adamawa state coordinator for the National Emergency Management Agency (NEMA), Sa'ad Bello, told AFP by telephone.

Suicide bombings that killed 58 at a camp for those who fled Boko Haram have raised doubts about the true extent of Nigeria's grip on security in the troubled northeast and its policy of returning the displaced.

President Muhammadu Buhari and his government have said many of the estimated two million internally displaced people (IDPs) can begin to return, as the military now has the upper hand.

Nigerian President Muhammadu Buhari urged the international community on Wednesday to help end the turmoil in Libya, warning that it was creating a "strategic time bomb" for Africa and Europe.

In a speech to the European Parliament, Buhari said the situation in lawless southern Libya was particularly alarming as it was creating a flow of arms affecting Nigeria and other countries.

Donors at the African Union summit pledged on Monday $250 million (229 million euros) for the fight against Boko Haram insurgents, AU Peace and Security Council chief Smail Chergui said.

Boko Haram, facing the heat of a military onslaught in Nigeria, has in the past year stepped up cross-border attacks in Niger, Chad and Cameroon, while continuing shooting and suicide assaults on markets, mosques and other mostly civilian targets within Nigeria itself.