A cargo plane carrying the remains of 74 South Africans killed in a building collapse in Nigeria landed in Pretoria on Sunday, two months after the accident.

A total of 116 people -- including 81 South Africans --  were killed on September 12 when a multi-storey guesthouse collapsed at a Lagos mega-church.

Everyday they cross the border from Nigeria on motorbikes, donkeys or even on foot, and all are looking for safe haven from the Islamist militants of Boko Haram. 

They arrive at the already teeming refugee camp in Minawao in northern Cameroon, where they join the thousands of Nigerians who have fled the insurgency in their home country that's killed some 10,000 people.

Six people, including three police, were killed in a suspected Boko Haram suicide attack at a petrol station in Nigeria's biggest city, Kano, police said on Friday.

"A man driving a Toyota Sienna drove into the filling station as if he was going to buy fuel. The vehicle exploded causing six deaths, including three policemen," the Kano state police commissioner Adelenre Shinaba told reporters.

Boko Haram has seized the northeastern Nigerian town of Chibok, from where 276 girls were kidnapped more than six months ago and which the government vowed to secure after the mass abduction.

The April 14 kidnapping in the impoverished town in southern Borno state brought unprecedented global attention to the armed Islamist group's brutal five-year uprising.

Nigeria on Friday said three servicemen were killed in a military helicopter crash in the restive northeast, while Boko Haram rebels raided two more towns and vigilantes and hunters clawed back a key militant stronghold.

The second crash in a week happened late on Thursday in Yola, the capital of Adamawa, which is one of three states that has been under emergency rule since May last year.

The U.N.'s special representative for central Africa on Thursday called on increased international support in the struggle against Boko Haram, with thousands of Nigerians having fled and cross-border attacks on the rise.

"Deadly attacks by Boko Haram have gone beyond Nigeria's borders and now constitute a threat for neighbouring countries," Abdoulaye Bathily told reporters in the Gabon capital Libreville.

The United States hit back Wednesday at allegations by the Nigerian ambassador of failing to help fight Boko Haram militants, saying there had been "a great deal" of U.S. aid to his country.

In the past six months since the Islamic militants snatched some 200 schoolgirls in northern Nigeria, Washington has shared intelligence with the Nigerian army, begun training a new battalion and held high-level talks on the threat of Boko Haram, a U.S. official said.

The death toll in a suspected Boko Haram suicide bombing of a secondary school in northeast Nigeria has risen to 58, a school official told AFP on Wednesday.

"From records at our disposal, the death toll now stands at 58 while the number of those injured has soared to 117," said the official at the school in Potiskum, Yobe state.

At least 10 people were feared dead on Wednesday after an suspected suicide bombing rocked a teacher training college in northwest Nigeria as students were sitting exams, police and a student said.

The blast happened at the Federal College of Education in the town of Kontagora, Niger state, some 150 kilometers (90 miles) from the state capital, Minna.

Nigeria's ambassador to Washington has blasted the United States for refusing to sell his country the weapons needed to deliver "the killer punch" to defeat Boko Haram militants.

In a speech made public Tuesday, Ambassador Adebowale Adefuye also dismissed as "rumors, hear-says and exaggerated accounts" allegations of human rights abuses by the Nigerian army in its crackdown on the Islamist extremists.