At least 15 civilians have been killed in a suicide bombing by suspected Islamist militants in north-east Nigeria, officials say.

Six of the attackers also died in the explosion, which took place on the outskirts of the city of Maiduguri, a defence ministry spokesman said.

Authorities said the Boko Haram group was behind the assault.

At least 1,500 lives have been claimed in the restive north-eastern region this year, according to latest figures.

Half of those killed were civilians, Amnesty International said in a report released on Monday.

The organisation blamed both “an increase in attacks by Boko Haram and uncontrolled reprisals by Nigeria’s security forces” for the high death toll.

Tuesday’s explosion happened when a militant blew up a vehicle near a checkpoint in Borno state, the defence ministry said.

The blast took place as soldiers were trying to foil the militants’ attempt to drive several vehicles with explosives into a petrol station, spokesman Brig Gen Chris Okulade told journalists.

“Three explosive-laden vehicles were demobilised by shots fired at them by soldiers at the checkpoint,” he said.

But a fourth car exploded, apparently set off by one of the militants.

Boko Haram was launched in Maiduguri in 2009, with the aim of setting up an Islamic state.

A state of emergency was declared in three north-eastern states last year to help the military crush the insurgency.

However, the militants have stepped up attacks in recent months.

The violence has forced some 250,000 people from their homes so far this year, according to Nigeria’s relief agency.

More than three million people are said to face a humanitarian crisis.

•Credit (except headline): BBC. Photo shows Nigerian troops hunting terrorists in Borno State.