Boko Haram believed to be behind attack on medics in Potsikum, beheading one, week after nurses murdered in Kano

Assailants in north-eastern Nigeria have killed three North Korean doctors, beheading one of the physicians, in the latest attack on health workers in a nation under assault by a radical Islamic sect, officials said on Sunday.

The deaths on Saturday night of the doctors in Potiskum, a town in Yobe state, comes after gunmen killed at least nine women administering polio vaccines in Kano, the major city of Nigeria's predominantly Muslim north.

The two attacks raise questions over whether an extremist, sect Boko Haram, has picked a new soft target in its guerrilla campaign of shootings and bombings across the country. The sect has carried out a number of attacks in Yobe in the past 18 months.

The attackers apparently attacked the North Korean doctors inside their home, said Dr Mohammed Mamman, chairman of the hospital managing board of Yobe state. The doctors had no security guards at their residence and typically travelled around via three-wheel taxis without a police escort, officials said.

By the time soldiers arrived at the house, they found the doctors' wives cowering in a flowerbed outside their home. At the property, they found the corpses of the men, all bearing what appeared to be machete wounds.

An AP journalist later saw the doctors' bodies before they were moved to nearby Bauchi state for safe keeping. Two of the men had their throats slit, the other was decapitated.

The doctors were living in a quiet neighbourhood of the town because there was not room to house them at the hospital, where they would have had some security protection, Mamman said.

He told journalists that the three men were from North Korea and had lived in the state since 2005 as part of a medical programme between Yobe and the Pyongyang government.

There are more than a dozen other North Korean doctors posted to the state under the scheme, which also includes engineers, Mamman said. He said all will receive immediate protection from security forces. "It is very unfortunate," he said of the killings.

Yobe state's police commissioner, Sanusi Rufa, said officers had made 10 arrests after the killings. Police in Nigeria routinely round up those living around the site of a crime, whether or not there is any evidence against them.

No one claimed responsibility for the attack, though suspicion fell on the Boko Haram sect.

Boko Haram, whose name means "western education is sacrilege," has been attacking government buildings and security forces over the last year and a half. In 2012, the group was blamed for killing at least 792 people, according to a count by AP.

The sect, which typically speaks to journalists in telephone conference calls at times of its choosing, could not be reached for comment. In recent months, however, Boko Haram has not claimed any attacks, raising questions about whether it had splintered into smaller, independently operating groups.

Boko Haram has carried out attacks in Potiskum since late 2011, killing dozens at a time. As a response there is a heavy contingent of police officers and soldiers deployed in the town.

For the last few weeks, however, Potiskum, which is 500km (300 miles) north-east of the Nigerian capital, Abuja, has been quiet. Soldiers still mount a series of checkpoints throughout the town, where in the past the military has put neighbourhoods in lockdown and launched door-to-door searches for militants.

Pyongyang's official Korean Central News Agency did not immediately report the three doctors' deaths.

The killings come after the attack last Friday on polio vaccinators in Kano, northern Nigeria's most populous city. No group has yet claimed responsibility for that attack either.

Boko Haram has allegedly been behind the destruction of lightly guarded mobile phone towers, limiting the ability of residents and security forces to call for help during attacks, as well as cutting the government's ability to use the signals to track suspected militants.