At least 26 people have been killed in bombings in two major cities in northern Nigeria, emergency workers and witnesses say.

The first blast at bus rank in Gombe killed at least 20 while another six died in an explosion at a market in Bauchi, they added.

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.

They were made to lay face down before being shot dead.

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.

'Training camp dismantled'

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 body parts lay scattered at the site of the blast in Gombe.

Government official Mato Yakubu said the explosion occurred, as people were climbing on to a nearby bus at the Dukku bus park, AFP news agency reports.

Mr Gombe said he expected the number of people killed by the explosion to rise.

Eighteen people had been rushed to hospital with serious injuries, he added.

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 Bauchi state as well as Adamawa, Borno and Yobe, the three Nigerian states worst-affected by the insurgency and which have been under emergency rule since last year.

The explosion in Bauchi city had caused a huge fire, and there were "heavy casualties", the Red Cross said.

On Sunday, Cameroon's military said it had dismantled a training camp run by Boko Haram in the Guirvidig locality near its border with north-eastern Nigeria.

Soldiers captured 45 trainers and 84 children between the ages of seven and 15 who were undergoing training, a spokesman for the Ministry of Defence, Lieutenant Colonel Didier Badjecks, told the Reuters news agency.

He said "many more" had been killed in the raid.

Boko Haram launched its insurgency in Nigeria in 2009 to create an Islamic state in the region.

At least 2,000 civilians have been killed by the group in Nigeria this year.

The kidnapping of more than 200 schoolgirls by Boko Haram in April from the town of Chibok in Borno state sparked international outrage.