A measles outbreak in Democratic Republic of Congo's copper-mining southeast has killed 428 people and infected about 30,000 since the start of the year, the United Nations said on Friday.

More than 100 deaths and 10,000 additional cases have been recorded since mid-August, when the United Nations committed $2.4 million to fight the outbreak in the former province of Katanga, which was recently divided into four.

Humanitarian groups said the money was not enough and poor roads and health services in the region were hindering vaccination drives.

"We have contained the disease somewhat in the short term," Yvon Edoumou, spokesman for the U.N. Office for the Coordination of Humanitarian Affairs (OCHA), told Reuters. "But it's sad to see that the disease is still progressing."

The outbreak is the country's worst since 2010-11, when 1,085 people died and about 77,000 were infected in Katanga.

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The industrial copper and cobalt mining parts of the region, Africa's leading producer of both metals, have largely escaped the outbreak.

Measles is a highly contagious virus that can lead to deadly complications like diarrhea, dehydration, respiratory infection and encephalitis.

Mortality rates can be as high as 20 percent in poor countries, according to medical charity Medecins Sans Frontieres, even though it only costs about $1 to vaccinate a child.

The World Health Organization warned last November that progress toward wiping out measles has stalled worldwide due to poor vaccine coverage.