Abuja - Fifteen civilians were killed in an explosion in northeast Nigeria on Tuesday, after troops foiled what the military said was an attempted suicide attack by Boko Haram Islamist militants.
Among the dead was a member of a civilian vigilante group assisting soldiers in their attempt to put down the insurgency, which has claimed more than 1,500 lives this year alone.
Defence spokesman Chris Olukolade said the blast in Mulai, on the outskirts of Boko Haram's spiritual heartland, Maiduguri, destroyed eight vehicles.
"Six of the terrorists died while one has been arrested," he added in a statement, describing it as a "suicide attack".
The military had said earlier that soldiers "demobilised" three out of four explosives-laden cars that the militants were planning to explode at a petrol station.
But a blast then ripped through the area, killing four Boko Haram fighters and wounding five soldiers.
Initial reports indicated that the troops stationed at the checkpoint on the Maiduguri-Damboa road were the target.
But eyewitnesses 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 that have hit the country.
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.
- War crimes allegations -
The unrest has killed thousands of people since 2009.
Since the start of the year, more than 250,000 people have been displaced by the conflict in three states: Borno, of which Maiduguri is the capital, neighbouring Yobe and Adamawa, Nigeria's main relief agency said last month.
The three states have 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 defenceless civilians and schoolchildren among those slaughtered in recent weeks.
The upsurge in violence has prompted questions about the military's strategy, with criticism that its use of conventional force against largely guerrilla tactics has been ineffective.
The military has attributed the wave of attacks to an enemy lashing out because a troop surge has left them without arms, ammunition and men and cut off their escape routes to safe havens in neighbouring countries.
On Sunday, 21 suspected Boko Haram detainees were killed in an attempted jail break from the headquarters of Nigeria's intelligence agency, the Department of State Services in Abuja.
Amnesty International said on Monday that more than 1,500 people had died in the conflict in the first three months of this year and that both sides in the conflict may have committed war crimes and crimes against humanity.
The human rights group, which wants an independent investigation into the claims, alleged that troops killed hundreds of Boko Haram suspects who escaped from a detention facility at a military barracks in Maiduguri on March 14.