Men armed with knives slit the throats of three North Korean doctors in a pre-dawn attack Sunday in a volatile town in northeastern Nigeria in the latest in a spate of such killings in recent months, police said.
The attack in Potiskum also came just two days after gunmen killed at least 10 people in horrifying attacks on two Nigerian polio clinics in a new blow to the campaign to wipe out the disease, but it was not clear if the incidents were related.
Yobe State police commissioner Sanusi Rufa'i would not say if the Islamist group Boko Haram, which has been active in Potiskum, was responsible for Sunday's killings, but that the attack was being investigated.
He said unknown attackers scaled the fence of an apartment housing the three doctors at around 1:00 am and slit their throats, initially describing the victims as Chinese, then as South Koreans, before finally saying they were from North Korea.
"The three men were from North Korea and not South Korea," Yobe state police commissioner Sanusi Rufa'i told AFP. "They were doctors working in Potiskum on behalf of the state government."
Abdullahi Bego, spokesman for the Yobe state governor, also identified the victims as North Koreans and said they were in Nigeria as part of a cooperation agreement signed some five years ago.
North Korean embassy officials could not be reached for comment.
A local resident said the bodies of the Koreans were found in their room by neighbours who alerted security agents.
"People became worried when the doctors did not open their door in the morning," one resident who did not want to be named told AFP.
He said the victims had their throats slit, but it was not immediately clear if the assailants also came with guns.
"It is still premature to point any accusing fingers but we have commenced an investigation to unravel the killings," said Rufa'i, adding: "No arrest has been made."
Sunday's attack was the latest in a spate of killings of foreigners, especially Chinese nationals, in the country's restive northeast.
In November, gunmen shot dead two Chinese construction workers in nearby Borno State, the stronghold of the Boko Haram extremists.
Three other Chinese nationals have also been killed in separate attacks in the region.
A number of Nigerian victims have also had their throats slit in the region in recent months.
Although no group claimed responsibility for the attacks, they were similar to previous Boko Haram strikes against foreigners.
Violence linked to Boko Haram is believed to have left some 3,000 people dead since 2009, including killings by the security forces.
The killings in Potiskum, which lies about 100 kilometres (60 miles) from the state capital Damaturu, followed attacks on other health workers in the northern city of Kano on Friday.
Nine women and a man were shot dead in two separate attacks in Kano after a local cleric denounced polio vaccination campaigns and some local radio stations aired conspiracy theories about the vaccine being a Western plot to harm Muslims.
Nigerian President Goodluck Jonathan condemned Friday's killings, describing them as "dastardly terrorist attacks" and vowed to track down the perpetrators.
Boko Haram has claimed to be fighting for the creation of an Islamic state, but its demands have shifted repeatedly and it is believed to include various factions. Criminal gangs and imitators are also suspected of carrying out violence under the guise of the group.
Nigeria, Africa's most populous nation and largest oil producer, is divided between a mainly Muslim north and predominantly Christian south.
