JOHANNESBURG: Boko Haram leader Abubakar Shekau has claimed responsibility for the mass killings in the Northeast Nigerian town of Baga and has threatened more violence.

The acknowledgement from the leader of Nigeria's Islamic extremists comes in a video posted on YouTube Tuesday, the same day International Criminal Court prosecutor Fatou Bensouda said she is examining the allegations and will prosecute those most responsible for war crimes.

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According to a translation from Arabic provided by SITE Intelligence Group, Shekau says: "We are the ones who fought the people of Baga, and we have killed them with such a killing".

Amnesty International had said as many as 2,000 civilians were killed and 3,700 homes and business were destroyed in the Jan 3 attack. Baga and a key military base remain under Boko Haram's control.

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"This marks a disturbing and bloody escalation of Boko Haram's ongoing onslaught," said Daniel Eyre, Nigeria researcher for Amnesty International.

In Washington, US State Department Spokesman Jen Psaki had condemned the attacks.

“We urge Nigeria and its neighbours to take all possible steps to address the urgent threat of Boko Haram. Even in the face of these horrifying attacks, terrorist organisations like Boko Haram must not distract Nigeria from carrying out credible and peaceful elections that reflect the will of the Nigerian people,” Psaki had said in a statement.