In another spasm of violence, three foreign doctors have been killed in northeastern Nigeria. The deadly attack comes just days after nine women nurses administering polio vaccines were murdered by suspected Islamists.
Assailants in northeastern Nigeria have killed three North Korean doctors, cutting the throats of two and beheading a third.
The doctors' deaths early Sunday morning in Potiskum, Yobe state, came after gunmen killed nine women involved in administering polio vaccines in Kano, northern Nigeria's main city, on Friday.
DW's Sam Olukoya in Lagos said the Nigerian Medical Association warned on Monday that health workers would pull out from areas where their security cannot be guaranteed.
No group has yet claimed responsibility for both attacks, but suspicion has fallen on the militant Islamist Boko Haram sect. The group was blamed for the deaths of at least 790 people in 2012 alone.
Dr Mohammed Mamman, chairman of Yobe state's hospital managing board, said the attackers struck the North Korean doctors inside their home. The corpses all had what appeared to be machete wounds, he added. When soldiers arrived at the doctors' house, they found the men's wives cowering on a flower bed outside the home, he told reporters.
Mamman said the doctors had lived in Yobe state since 2005 and were part of a technical exchange between the state and the North Korean government.
The men had no security guards at their residence and typically travelled around Potiskum in three-wheel taxis without a police escort, local law enforcement officials said.
Friday's attack on foreign polio workers in Kano was condemned by Nigerian President Goodluck Jonathan who said efforts to cut child mortality wouldn't be stopped by "mindless acts of terrorism."
Nigeriais only one of three countries, along with Pakistan and Afghanistan, still considered to have endemic polio. It predominantly afflicts children under the age of five, causing paralysis, crippled limbs and in some cases death.
The president's statement on Friday had promised "enhanced security measures to be put in place for health workers in high-risk areas."
But that did not deter the attackers in Potiskum, and did not stop them slipping away unnoticed after killing the three doctors.
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, prompting the Chinese government to ask Nigerian officials to provide better protection for their citizens.
North Korean embassy officials in Nigeria could not be reached for comment.