Boko Haram razed at least 16 towns and villages in northern Nigeria and may have killed up to 2,000 people since the weekend, officials said Thursday.

After capturing a key military base in northeast Nigeria on Saturday, members of the feared armed group used crude bombs to level entire towns, according to local authorities.

District head Baba Abba Hassan said most victims are children, women and elderly people who could not run fast enough when insurgents drove into Baga, firing rocket-propelled grenades and assault rifles on residents.

"The human carnage perpetrated by Boko Haram terrorists in Baga was enormous," Muhammad Abba Gava, a spokesman for poorly armed civilians in a defense group that fights Boko Haram, told The Associated Press.

He said civilian fighters gave up on trying to count all the bodies. "No one could attend to the corpses and even the seriously injured ones who may have died by now," Gava said.

Musa Bukar, head of the Kukawa local government area, told BBC News 16 communities were “burned to the ground” and that corpses were strewn across Baga, the site of a Nigerian military base.

Ahmed Khalifa, another Borno state lawmaker, told NBC News that the "towns are just gone." More than 2,000 people, he said, were missing, and "the whole area is covered in bodies.”

The 2,000 death toll hasn't been officially confirmed.

The 5-year insurgency killed more than 10,000 people last year alone, according to the Washington-based Council on Foreign Relations. More than a million people are displaced inside Nigeria and hundreds of thousands have fled across its borders into Chad, Cameroon and Nigeria.

Abubakar Gamandi, head of Borno's fish traders union and a Baga native, confirmed the attacks and said that hundreds of people were now trapped on islands on nearby Lake Chad.

"They told me that some of them are dying from lack of food, cold and malaria on the mosquito-infested island," he said. "I was in constant touch with them until this morning when the phone they were using went off, which I assume was due to dead battery.”

Boko Haram fighters on Saturday captured Baga, which houses the headquarters of the Multinational Joint Task Force (MNJTF) made up of troops from Nigeria, Niger and Chad.

Security analysts this week said that Baga was of strategic importance for Boko Haram, as it was thought to be the last town in northern Borno under federal government control.

The fighters, who have seized more than two dozen towns in northeast Nigeria in the last six months, now control all three of Borno's borders with Niger, Chad and Cameroon.

News of the latest attacks came as Nigeria's President Goodluck Jonathan, who has been criticized for his inability to end the insurgency, formally launched his re-election campaign.

Nigeria's military — West Africa's largest — has come under scrutiny for its inability to fight the armed group after reports of a lack of adequate weaponry and even bullets.

Boko Haram, in contrast, has been seen with advanced weapons, including rocket-propelled grenades, heavy machine guns and even a tank.

Al Jazeera and wire services