POTISKUM, Nigeria -- Assailants in northeastern Nigeria 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 Sunday.
The deaths Saturday night of the doctors in Potiskum, a town in Yobe state long under attack by the sect known as Boko Haram, 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 new questions over whether the extremist sect, targeted by Nigeria's police and military, has picked a new soft target in its guerrilla campaign of shootings and bombings across the nation.
The attackers apparently struck at the North Korean doctors inside their home, said Dr. Mohammed Mamman, chairman of the Hospital Managing Board of Yobe State. The North Korean doctors had no security guards at their residence and typically traveled around the city 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 flower bed outside their home. At the property, they found the corpses of the men, all bearing what appeared to be machete wounds.
An Associated Press journalist later saw the North Korean doctors' corpses before they were moved to nearby Bauchi state for safe keeping. Two of the men had their throats slit. Attackers beheaded the other doctor.
The doctors lived in a quiet neighborhood filled with other modest homes in the town. There wasn't room to house them at the hospital, where they would have had some security protection, Mamman said.
Initially, doctors at the hospital who worked with the physicians identified them as being from South Korea, while police identified the dead as being from China. Ultimately, Mamman of the health board told journalists those killed were from North Korea and had lived in the state since 2005 as part of a technical exchange program between the state and the North Korean government.
There are more than a dozen other North Korean doctors posted to the state under the program, as well as engineers, Mamman said. He said all will receive immediate protection from security forces.
"It is very unfortunate," Mamman said of the killings.
Yobe state police commissioner Sanusi Rufai confirmed the attack took place and said officers had begun an investigation. Rufai said officers had made 10 arrests after the killings, though police in Nigeria routinely round up those living around the site of a crime, whether or not there is any evidence suggesting their complicity.
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 alone, the group was blamed for killing at least 792 people, according to an AP count.
The sect, which typically speaks to journalists in telephone conference calls at times of its choosing, could not be reached for comment Sunday. In recent months, however, Boko Haram has not claimed any attacks, raising questions about whether the shadowy sect that already had a loose command-and-control structure had splintered into smaller, independently operating terror groups.
Since late 2011, Potiskum, about 500 kilometers (300 miles) northeast of Nigeria's central capital, Abuja, has been targeted by Boko Haram fighters in attacks. The attacks killed dozens at a time and brought the deployment of a heavy contingent of police officers and soldiers to the town.
For the last few weeks, however, Potiskum has been quiet. Soldiers still mount a series of checkpoints throughout the town, where in the past the military has put neighborhoods in lockdown and launched door-to-door searches for militants.
Oil-rich Nigeria, home to more than 160 million people, maintains diplomatic relations with North Korea, which faces international criticism over its nuclear weapon program. In October, a delegation of Nigerian officials led by Minister of State for Foreign Affairs Viola Onwuliri visited North Korea.
Pyongyang's official Korean Central News Agency did not immediately report the three doctors' deaths Sunday. In Pyongyang earlier Sunday, North Koreans marked the Lunar New Year with pilgrimages to the giant statues of their late leaders.
Foreigners have been targets for such attacks in the region in the past. Several Chinese construction workers have been shot dead in recent months around the northeastern city of Maiduguri. That prompted the Chinese government to contact Nigerian officials and ask them to provide better protection for their citizens.
The killings of the doctors come after the attack Friday on polio vaccinators in Kano, northern Nigeria's most populous city. No group has yet claimed responsibility for that attack either, though it follows alleged Boko Haram attacks now focusing on softer targets, like lightly guarded mobile phone towers. Those mobile phone tower attacks have limited the ability of residents and security forces to call for help during attacks, as well as have cut the government's ability to use the signals to track suspected militants.
In a statement Friday, President Goodluck Jonathan condemned the killings of the polio workers and promised that efforts to cut child mortality wouldn't be stopped by "mindless acts of terrorism."
"While the government will continue to do everything possible to track down and apprehend agents of terrorism in the country, the president has directed that enhanced security measures be put in place immediately for health workers in high-risk areas," the statement read.
Despite that promise, however, attackers were able to kill the North Korean doctors and apparently slip away. Reuben Abati, a presidential spokesman, did not respond to a request for comment Sunday.
Associated Press writers Jon Gambrell in Johannesburg and Hyung-Jin Kim in Seoul, South Korea, contributed to this report.