A woman from who was in the middle of giving birth to a baby boy was reportedly killed by militants belonging to Boko Haram last week, witnesses said.

Boko Haram began attacking towns and villages in the Baga area on January 3 "for their perceived collaboration with the security forces", said Amnesty International.

A witness told the group that during the Baga attack, militants were aggressively seeking Civilian Joint Task Force members and were particularly shooting men of fighting age.

Amnesty International revealed that Boko Haram fighters started the attack with indiscriminate firing, and that the woman in labour was shot along with several other children.

"Half of the baby boy was out and she died like this," an unnamed witness shared.

The brutal massacre in Baga area reportedly claimed the lives of over 2,000 people.

"They killed so many people. I saw maybe around 100 killed at that time in Baga. I ran to the bush. As we were running, they were shooting and killing," another witness said.

Daniel Eyre, Nigeria researcher of Amnesty International reported that of all Boko Haram assaults analysed by Amnesty International, this was "the largest and most destructive yet".

"It represents a deliberate attack on civilians whose homes, clinics and schools are now burnt out ruins," he said.

The Nigerian government has denied that the death toll has reached thousands, and insisted that it numbers below 150.

But pictures collected by Amnesty International and the testimonies they obtained from survivors indicate otherwise.

According to Amnesty, over 3,700 structures were either damaged or completely destroyed.

The attacks conducted on neighbouring towns Baga and Doron Baga were so extensive and devastating that they were "almost wiped off the map in the space of four days," said Eyre.