Two Sudanese health ministry workers helping to vaccinate children in the Darfur region have been killed, the United Nations said on Saturday, condemning their deaths.
The victims, a vaccinator and a driver, were part of a team inoculating vulnerable children against measles in West Darfur state, Ali Al-Za'tari, the UN's chief in Sudan, said in a statement.
"I call on all parties to ensure the protection of all personnel working to deliver assistance to populations in need throughout Sudan," Za'tari said.
His statement gave no details of the attack but UN sources told AFP the incident appeared to be a carjacking.
Gunmen ordered the health workers to hand over their vehicle and "when they refused, that's when they killed them," said one source, on condition of anonymity.
The attack happened last Monday.
Violence has worsened in Darfur, where at least 460,000 people have been displaced by fighting this year, the United Nations says.
While battles between the government and rebels continue, Defence Minister Abdelrahim Mohammed Hussein said this month that violence between rival Arab tribes has eclipsed rebel activity as the main security threat.
The fighting, over land and other resources, has involved heavy weapons including rockets.
Non-Arab rebels rose up in Darfur 10 years ago, seeking an end to what they viewed as Arab elites' domination of Sudan's power and wealth.
In response, government-backed Janjaweed militiamen, recruited among the region's Arab tribes, shocked the world with atrocities against civilians.
Analysts say the cash-starved Khartoum government can no longer control its former Arab tribal allies.
Government-linked militia are suspected of carrying out many of the carjackings, kidnappings and other crimes that blight the region.
The deaths of the two health workers bring to six the number of Sudanese aid staff killed in Sudan this year, according to an AFP tally.
Carjackers killed an aid worker southwest of Nyala city in October, while the other victims were killed by stray fire during fighting between rival groups.
The health ministry began a nationwide measles vaccination campaign on November 24 targeting about 15 million children.
The number of cases of the disease in Sudan dropped by 95 percent after previous innoculation campaigns but has risen since 2010, the UN says.
"Subsequently, measles has spread across the country," the UN Office for the Coordination of Humanitarian Affairs said in its latest weekly bulletin.
"This high level of transmission continues."