A suicide bomb attack has killed more than a dozen people at a crowded bus station in Potiskum, north-eastern Nigeria.

A witness told the BBC that a bomber tried to board a bus as transport officials were loading it.

Hospital sources say 13 corpses have been taken to the town's mortuary and more than 30 people have been injured.

It is the second attack on Potiskum in recent days. Both have been blamed on the militant group Boko Haram.

The Kano-bound bus was completely destroyed and other vehicles at the Dan-Borno bus station were also affected in Tuesday's explosion.

Although no group has claimed responsibility for the latest attack, Boko Haram has stepped up suicide bombings against civilians in recent months.

On Sunday, a young girl with explosives strapped to her killed five people and wounded dozens at a security checkpoint outside a market in Potiskum.

Boko Haram now controls vast swathes of north-east Nigeria and has displaced over 1.5 million people.

The mounting threat of the Islamist insurgency has already led to postponement of February's presidential elections, with the vote now due to take place on 28 March.

The delay is designed to give the Nigerian military time to re-establish its presence in the area. However, opponents of President Goodluck Jonathan have claimed that the delay is actually a political tactic.

The group is under increased pressure from the Nigerian troops as well as those of Chad, Niger, and Cameroon.