BAUCHI/MAIDUGURI, Nigeria (Reuters) - Islamist militant group Boko Haram has said it was behind Monday’s twin suicide bombing at a university in north eastern Nigeria which killed two people.

A video featuring an audio recording purporting to be leader Abubakar Shekau was posted on social media late on Monday. Reuters was unable to verify if the voice was indeed his.

“The bomb that exploded on Monday morning, it’s our brothers responsible for it,” the recording said.

A professor at the University of Maiduguri and a child were killed and 17 people wounded in a twin suicide bombing, officials said on the day of the attack.

The group has stepped up attacks in the past few weeks as the end of the rainy season facilitates movements in the bush. Maiduguri is the provincial capital of northeast Nigeria’s Borno state and the epicenter of Boko Haram’s seven-year armed attempt to create a regional Islamic caliphate.

Boko Haram’s insurgency has killed about 15,000 people and displaced more than 2 million. In early 2015, the group controlled an area the size of Belgium but has been pushed out from most of territory by the Nigerian military with help from neighboring countries.

The group split in two last year, with one faction led by Shekau from the Sambisa forest and the other, allied to Islamic State and led by Abu Musab al-Barnawi, based in the Lake Chad region.