Three North Korean doctors were killed by suspected Islamists in northeast Nigeria’s Yobe state, local authorities said on Sunday.

“It is true. The three doctors were slaughtered while sleeping in their house,” Nigeria’s Yobe state police commissioner, Sanusi Rufai, was quoted by spyghana.com as saying.

Two doctors had their throats cut and the third one was beheaded. The bodies were found on Sunday morning in their flat in Nigeria’s city of Potiskum. The medics were working at a government-run hospital.

No one has claimed responsibility for the attack, though the Islamist militant group, Boko Haram, which has been active in the country’s north, is suspected of being behind the murder.

The murder comes two days after nine female health workers conducting anti-polio vaccination were killed by gunmen in Kano, in Nigeria’s predominantly Muslim north.