The disease is believed to have infected 194 people and killed 122 since the outbreak started in eastern Congo in July, according to the health ministry.

The number of new cases per day has more than doubled since September, partly because worsening security is hampering the response, said the International Rescue Committee.

The outbreak is centred in the city of Beni, where rebels killed at least 18 people in an attack last month, forcing health workers to suspend operations for several days.

Four civilians were killed in another attack near Beni on Tuesday, according to the United Nations. The IRC again suspended programs on Wednesday, resuming on Thursday afternoon but only within Beni city limits, a spokeswoman said.

"The current spike in Ebola cases and deaths is extremely worrying," said Michelle Gayer, IRC's senior director of emergency health, on Thursday.

"It's likely that the forced suspension in programming due to insecurity and community resistance in and around Beni are major factors in this," she said.

The region has been a tinder box of armed rebellion and ethnic killing since two civil wars in the late 1990s.

Community resistance has also caused violence, with angry villagers attacking Red Cross volunteers on several occasions and preventing a burial last week.

"We are concerned that (violence) is contributing to the rise in Ebola cases in Beni and that this could be the tipping point for an accelerated spread of the disease," Red Cross spokesman Euloge Ishimwe told the Thomson Reuters Foundation.

Conspiracy theories, fear and mistrust around the disease have caused people to resist help and hide symptoms, he said.

The outbreak is expected to last at least another three or four months but if insecurity continues there could be "a much larger wave building," said Peter Salama, emergency response chief of the World Health Organization, on Thursday.

Australian Associated Press