MAIDUGURI, Nigeria (Reuters) – Suicide bombers killed 17 people and injured 21 in the northeast Nigerian city of Maiduguri, the police commissioner of Borno state said on Wednesday.

It is the latest in a spate of suicide bomb attacks on the city in the last few weeks. Borno, of which Maiduguri is the capital, is the Nigerian state worst affected by the eight-year-old insurgency by Islamist militant group Boko Haram.

Witnesses said four suicide bombers carried out attacks in the Molai district, which is around 5 kilometers from the city center, on Tuesday night at around 10:00 p.m. (2100 GMT). Nobody has claimed responsibility for the attacks.

Damian Chukwu, the Borno state police commissioner said the suicide bombers were among the 17 killed.

Boko Haram, which has killed more than 20,000 people and forced some 2.7 million people to flee their homes in its bid to create an Islamic state.

The group has been pushed out of most of a swathe of land around the size of Belgium that it controlled in early 2015 by the Nigeria’s army and troops from neighboring countries in the northeast Nigeria.

But insurgents continue to carry out suicide bombings and raids in northeast Nigeria, as well as in Cameroon and Niger.

(Reporting by Ahmed Kingimi and Lanre Ola; Writing by Alexis Akwagyiram; Editing by Toby Chopra)