A bomb attack on a packed market in north-eastern Nigeria bearing the hallmarks of Boko Haram has killed around 50 people.

The explosion hit the town of Sabon Gari in Borno state, which is the heartland of the Islamist militant group.

Umar Kidda, a member of a civilian vigilante group who witnessed bodies being taken away, said the market was busy when the explosion occurred.

A military source said around 50 people had been killed.

The US State Department strongly condemned what it said was a terrorist attack in Borno.

Boko Haram has killed thousands of people during a six-year armed campaign to set up an Islamic state in northeastern Nigeria.

More than 600 people have been killed in raids and bombings by the insurgents since President Muhammadu Buhari took office on May 29, promising to crush the group.