YOLA/BAUCHI, Nigeria (Reuters) - Suicide bombers killed at least six people and injured 14 in a crowded market in the northeastern Nigerian town of Madagali on Friday, the National Emergency Management Agency (NEMA) said.

A police spokesman had earlier said 15 were killed, and did not identify any suspects.

Suicide bombings are common in Nigeria’s northeast, the centre of a bloody campaign by jihadist group Boko Haram to create an Islamic state. Madagali was also hit last month, when schoolgirl suicide bombers killed as many as 56 people in a coordinated attack on a market.

Friday’s attacks, which bore the hallmark of Islamist militant group Boko Haram, followed a pair of bombings last week in Borno state, where the Boko Haram insurgency began, undermining a presidential announcement last month that the militants had been pushed out of their last stronghold in the northeast.

A man claiming to be Boko Haram leader Abubakar Shekau has appeared in a video denying President Muhammadu Buhari’s statement that the group had been ousted from the region.

Boko Haram’s seven-year-old insurgency, aimed at establishing a medieval-style caliphate in the northeast of Africa’s most populous nation, has killed about 15,000 people and displaced more than 2 million people.

Aid groups and international organisations now warn of a looming humanitarian crisis as people displaced by the insurgency are becoming vulnerable to disease and famine, even within camps set up to shelter them.

In early 2015, Boko Haram controlled an area about the size of Belgium, but has been driven out of much of it over the past year by Nigeria’s army and troops from neighbouring countries.

Boko Haram insurgents have since retreated to a base in the Sambisa forest, a vast former game reserve in Borno state.

Security analysts say the jihadists’ ability to carry out attacks in neighbouring Niger, Cameroon and Chad suggests that it has multiple bases.