In a brutal pre-dawn attack on health workers, armed men slit the throats of three North Korean doctors, beheading one of them, in the apartment they shared in Nigeria's volatile northern state of Yobe, police said.

"They invaded the apartment of the doctors... And slit their throats," Sanusi Rufai, the commissioner of police of Yobe state, said on the attack that occurred in the town of Potiskum.

"I can confirm to you that those killed are from North Korea and not Chinese or South Koreans," he said, clarifying the nationality of the slain physicians.

Residents say the slain North Korean doctors worked at a general hospital in the city. Two of them had their throats slit while the third was beheaded, they added.

The victims were reportedly found inside their flat this morning, after people became worried that they were not answering the door. Officials said the victims had been working at a government-run hospital.

No group has claimed responsibility for the attack.

Yobe shares border with Borno state where radical militant group Boko Haram has its headquarters.

Nigerian President Goodluck Jonathan condemned the killings and vowed that the campaign to eradicate polio would be carried through to a successful conclusion.

Last week, nine health workers on polio vaccination drive were shot dead by suspected Islamists in northern city of Kano. Potiskum has witnessed repeated attacks by the Boko Haram which has vowed to turn Nigeria into an Islamic state.

Boko Haram has a breakaway militant sect known as Ansaru which has attacked foreigners in the past.

More than 600 people were believed to have been killed in 2012 by the group, which is fighting to overthrow the government and create an Islamic state in Nigeria's predominantly Muslim north.

The slain doctors - two men and a woman - were giving technical assistance to the Yobe State Ministry of Health.

"The killing of innocent North Korean citizens who are in Yobe state to help the people with their expertise is rather unfortunate and the police must fish out the perpetrator of the ungodly act," Rufai told PTI on phone.

In July last year, two Indians were killed and one injured inside a factory by suspected members of Boko Haram in northern city of Maiduguri in Borno State.

In the recent past, seven Chinese have been killed in both Borno and Yobe states since the Boko Haram insurgency started in 2009.