Large areas of Nigerian towns attacked by Islamic extremists from Boko Haram were razed to the ground in a widespread campaign of destruction, according to satellite images released Thursday by Amnesty International.

Amnesty said the detailed images of Baga and Doron Baga in Borno state, taken before and after the attack earlier this month, show that more than 3,700 structures were damaged or completely destroyed.

Nigerian President Goodluck Jonathan, meanwhile, visited the capital of Borno in northeast Nigeria, where Boko Haram has increased attacks and seized more territory.

Jonathan's office said in a statement that the president traveled to Maiduguri in a "surprise visit" on Thursday and met troops involved in the fight against extremists. He also visited hundreds of civilians who were staying in a camp in Maiduguri after fleeing Baga, where Boko Haram fighters overran an army base and attacked civilians.

Jonathan, who is running for re-election in February, has not visited the northeast since a state of emergency was imposed in May 2014.

The satellite images released by Amnesty International were taken Jan. 2 and Jan. 7, the rights group said. Boko Haram fighters seized a military base in Baga on Jan. 3 and, according to witnesses, killed hundreds of civilians in the ensuing days.

Daniel Eyre, Nigeria researcher for Amnesty International, said in a statement that the assault on the Baga area was the largest and most destructive of all the Boko Haram assaults analyzed by Amnesty International.

The group said interviews with witnesses as well as local government officials and human rights activists suggest hundreds of civilians were shot; last week, the human rights group noted reports of as many as 2,000 dead. The Nigerian military has cited a figure of 150 dead, including slain militants.

Nigeria's home-grown Boko Haram group drew international condemnation when its fighters kidnapped 276 schoolgirls from a boarding school in northeast Chibok town last year. Dozens escaped but 219 remain missing.