Militant Islamists have carried out a wave of bombings in Nigeria since 2009
At least 20 people have been killed in a bombing at a bus station in Gombe city in north-eastern Nigeria, emergency workers say.
Body parts lay scattered across the scene after the explosion near a bus filling up with passengers, they said.
Militant Islamist group Boko Haram is waging an insurgency in the area.
Meanwhile, a video purportedly released by the group shows dozens of people being executed at a school dormitory after they were made to lay face down.
There is no independent confirmation that Boko Haram produced the video. It is unclear where or when it was shot.
But the video bears Boko Haram's insignia and shows gun-wielding men chanting "Allah is great" and speaking in the Kanuri language associated with the group's fighters, says BBC Nigeria analyst Jimeh Saleh.
Militants from Boko Haram, which means "Western education is forbidden", often attack educational establishments.
Red Cross official Abubakar Adamu Gombe told the BBC Hausa service that he expected the number of people killed by the explosion in Gombe to rise.
Eighteen people had been rushed to hospital with serious injuries, he said.
Government official Mato Yakubu said the blast occurred at 10:50 local time (09:50 GMT), as people were climbing on to a nearby bus at the Dukku bus park, AFP news agency reports.
At least three people were killed in a bomb attack at another bus station in Gombe city on 31 October.
Gombe state shares a border with Adamawa, Borno and Yobe, the three Nigerian states worst-affected by the insurgency and which have been under emergency rule since last year.
At least 2,000 civilians have been killed by Boko Haram this year.
The group launched its insurgency in 2009 to create an Islamic state in the region.
The kidnapping of more than 200 schoolgirls by Boko Haram in April from the town of Chibok in Borno state sparked international outrage.
