Boko Haram bombers have destroyed  a major bridge on a northeast Nigerian highway, further limiting access to base camps in the Sambisa Forest where scores of kidnapped girls are believed to be held captive, witnesses and the leader of a group fighting Boko Haram said Monday.

The Associated Press reported that gunmen destroyed most of the bridge on the road between Maiduguri and Biu on Saturday night, quoting the spokesman for the Nigerian Vigilante Group, Abbas Gava.

“The bridge has now collapsed and it is impossible for vehicles to cross over the bridge from either side,” he said. It is the fourth major bridge destroyed in the area in recent months.

Shekau, middle and his bombers in a new video shoot. AFP

The reports come as a new video shows Boko Haram leader Abubakar Shekau crowing over recent victories including two explosions at a fuel depot in Lagos that the government tried to cover up.

 At least four people died in the June 25 blasts, including an alleged female suicide bomber, according to Western diplomats who spoke on condition of anonymity because of the sensitivity of the issue.

Nigeria’s government, which often plays down insurgent attacks, said there was one explosion caused by a gas cylinder. But the diplomats said there is clear evidence of a car bomb exploding on the crowded road outside the depot, backed up with tankers, and of a person at the entrance gate believed to be a woman wearing a suicide bomb vest.

“We were the ones that detonated bomb in Abuja, that corrupt city,” Shekau says in the video of the first June 25 blast at the entrance to the biggest shopping mall in the capital in central Nigeria, which killed at least 21 people. It came hours before the explosions in Lagos, in the southwest of the country, that raise fears that the insurgency is spreading from its stronghold at the opposite end of the country in the northeast.

“We were responsible for the bomb in Kano, in Plateau. We were the ones that sent a female bomber to the refinery in Lagos,” Shekau says of other recent bombing in the video, which the AP obtained through similar channels used for previous messages.

He also repeats his demand that President Goodluck Jonathan release detained insurgents in exchange for more than 200 schoolgirls kidnapped three months ago.

“Nigerians are saying BringBackOurGirls, and we are telling Jonathan to bring back our arrested warriors, our army,” he says in the video.

The mass abduction from Chibok town before  on April 14 attracted international outrage and condemnation and led the United States and others to send counter-terrorism and hostage negotiation experts to Nigeria. The United States also has been flying unarmed drones, including over the Sambisa Forest, to try to help rescue the girls.