15 civilians killed in 'suicide attack' in Nigeria

Fifteen civilians were killed and 17 others were injured in a suicide attack in northeast Nigeria carried out by suspected Boko Haram militants, the military said on Tuesday.

Defense spokesman Chris Olukolade said one of the victims was a member of a civilian vigilante group and that the blast, on the outskirts of the capital of restive Borno state, Maiduguri, destroyed eight vehicles.

"Six of the terrorists died while one has been arrested," he added in a statement.

Earlier in the day, four would-be suicide bombers planning to blow up a petrol station died in Nigeria's troubled northeast after soldiers opened fire on their explosives-packed cars, the military and witnesses said.

The suspected Boko Haram Islamists were trying to attack a filling station owned by Nigeria's state oil firm on the outskirts of Maiduguri, the epicenter of a brutal insurgency which has already killed an estimated 1,500 people this year.

Olukolade said in a statement that "three of the four explosive-laden vehicles were demobilized by shots fired at them by soldiers".

Shortly after the officers opened fire an explosion "rocked the area", said Olukolade, adding that "four terrorists" died and five soldiers were wounded.

Initial reports indicated that the troops stationed at the checkpoint on the Maiduguri-Damboa road were the target.

But witnesses later said the attackers were trying to speed through the checkpoint so they could set off the blasts at the petrol station, which was backed up with vehicles because of fuel shortages across Nigeria, Africa's top oil producer.

Local residents said some soldiers or bystanders may have been killed by the blasts but there was no immediate confirmation.

Boko Haram was blamed for a series of blasts in Maiduguri last week that left at least five police officers and three civilians dead.

The group has repeatedly attacked the security services during an uprising aimed at creating a strict Islamic state in northern Nigeria. The unrest has killed thousands of people since 2009.

More than 250,000 people have been displaced by the conflict in the northeast since the start of the year, Nigeria's main relief agency said last month.

The entire region has been under a state of emergency since May 2013, when the military launched an offensive to wipe out Boko Haram.

But the results of the campaign have been mixed and brutal attacks have persisted, with defenseless civilians and schoolchildren among those slaughtered in recent weeks.