Five aid workers killed in Nigeria; president blames Boko Haram

July 23 (UPI) -- Five aid workers were killed after being abducted in Nigeria's Borno State last month, President Muhammadu Buhari said on Thursday.

Buhari blamed Boko Haram for the killings of the men who were working for Action Against Hunger, the International Rescue Committee, Rich International and Nigeria's State Emergency Management Agency.

He also vowed to bring the killers to justice and vowed to "wipe out the remaining vestiges" of Boko Haram.

Nigerian media shared video of the five victims being executed by hooded gunmen.

In another video released last month, the hostages referred to their captors as soldiers of the "khalifa" a term used to refer to Islamic State West Africa Province.

Action Against Hunger said it deeply regretted that its efforts to secure the release of the hostages had not been successful and the International Rescue Committee condemned the executions as "senseless" and "barbaric."

U.N. Secretary-General Antonio Guterres also condemned the killings and extended condolences to the families while calling on Nigeria to "spare no effort" in identifying and bringing the perpetrators to justice.

"The secretary-general reiterates that attacks by a party to an armed conflict that are directed against civilians including those who are aid workers, violate international humanitarian law," he said. "International human rights law and international humanitarian law must be fully respected, including the obligation to protect civilians."