POTISKUM, Nigeria — Attackers in northeastern Nigeria killed three South Korean doctors, beheading one of the physicians, in the latest onslaught targeting health workers in a nation under assault by a radical 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 newer, softer targets in its guerrilla campaign of shootings and bombings across the nation. The attackers apparently targeted the South Korean doctors inside their home, an official at General Hospital in Potiskum, a government-run health facility, told The Associated Press. The South Korean doctors had no security guards at their residence and typically traveled around the city via three-wheel taxis without a police escort, said the official who insisted upon anonymity because he is not authorized to speak to journalists. By the time soldiers arrived at the house, they found the doctors' wives cowering in a flower bed outside of their home, the official said. At the property, they found the corpses of the men, all bearing what appeared to be machete wounds. The AP journalist later saw the South 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. Yobe state police commissioner Sunusi Rufai confirmed the attack took place and said officers had begun an investigation. An official with South Korea's foreign ministry in Seoul declined to immediately comment when asked about the attack. 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 a count by AP, although more police officers and soldiers were sent to the norther by Nigeria's weak central government. The sect, which typically speaks to journalists in telephone conference calls at times of its choosing, could not be immediately reached for comment Sunday. The killings of the South Korean doctors comes 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. — AP