MAIDUGURI, Nigeria (Reuters) - A suicide bomber killed 14 people in northeast Nigeria, the state emergency agency said on Saturday, in an attack that bore the hallmarks of Boko Haram, days after a resurgence in the jihadist group’s activities prompted a shift in military tactics.

The attack in the town of Dikwa in Borno state came days after suspected members of the group kidnapped an oil prospecting team, prompting a rescue bid that ended in the deaths of at least 37 people including members of the team and rescuers from the military and armed vigilantes, officials say.

Three kidnapped members of the oil team appeared in a video seen by Reuters on Saturday, which was provided by suspected members of the militant group.

Boko Haram, which seeks to create an Islamic state in the northeast, has stepped up the frequency of attacks in the last few months. The insurgency has killed 20,000 people and forced some 2.7 million to flee their homes in the last eight years.

A suicide bomber detonated the explosives in Dikwa on Friday night, after entering a building housing people who had previously fled the insurgency and since returned, the State Emergency Management Agency (SEMA) said.

“We have so far evacuated 38 victims comprising 14 dead and 24 injured”, said SEMA spokesman Bello Dambatta. Dikwa is around 90 kilometers east of Maiduguri, the capital of Borno state.

The attack brings the number of people killed by insurgents in northeast Nigeria since June 1 to at least 113.

After the kidnapping of the oil workers, Acting President Yemi Osinbajo on Thursday sent military chiefs to the northeast to help regain control of the situation.

The move was a change of tactics since the government and military have repeatedly said Boko Haram - which also carries out cross-border attacks in neighboring Cameroon and Niger - was on the verge of being defeated.

President Muhammadu Buhari said in December that Boko Haram’s stronghold in the northeast’s vast Sambisa forest had been captured.