International aid agency Mercy Corps on Wednesday suspended its operations in two of the north eastern Nigerian states worst hit by Islamist insurgents after the army closed four of its offices in the region, the organisation said.

In a separate development in the northeast, another international aid agency – Action Against Hunger – said a hostage had been executed by a group that was holding one of its employees, two drivers and three health ministry workers.

Islamic State’s West Africa branch later claimed responsibility for the July kidnapping.

The developments come days after the army closed Action Against Hunger’s office in the region after accusing it of aiding terrorist groups such as Boko Haram and Islamic State.

Northeast Nigeria has been blighted by a decade-long insurgency led by militant group Boko Haram that has killed 30 000 people and forced two million to flee their homes. The United Nations has said 7.1 million people in the region need assistance in one of the world’s worst humanitarian crises.

“Mercy Corps is suspending operations in Borno and Yobe States, Nigeria, following the closure of four of our field offices by the Nigerian military,” said Amy Fairbairn, its head of media and communications, in a statement.

“We have not yet received an official reason from the Nigerian authorities for the closure and we are seeking to work with them to resolve this as soon as possible,” said Fairbairn, adding that Mercy Corps’ work in other parts of Nigeria would continue uninterrupted.

A military source and an aid worker at the organisation, both speaking on condition of anonymity, said the army closed the offices on Wednesday after troops said they had found $94 771 in cash being transported in north eastern Borno state by a driver who said the money belonged to Mercy Corps.