The Ebola ‌outbreak in Congo has not yet stabilised and is still expanding as population movement fuels transmission, a World Health Organisation official said on Tuesday.

The Democratic Republic of Congo has confirmed 1,561 cases, including ​506 deaths, in the worst-ever outbreak of the rare Bundibugyo species ​of Ebola, for which there is no proven treatment or ⁠cure.

"It is still in the expansion phase, unfortunately. We would like to ​say it is stabilising but, frankly, we cannot say it yet," Anne Ancia, ​WHO representative in Congo, told reporters by video link from Bunia, at the epicentre of the epidemic.

She said major challenges remained, such as the fact that some Ebola treatment centres were 90% full.

Another difficulty is that ​workers falling ill in the mining town of Mongbwalu are not seeking ​treatment locally, but instead travelling and spreading the disease to new regions, she said.

“It’s really ‌those people who are coming back, and coming back too late and going to die with their family," she said, adding that responders were trying to establish more checkpoints on roads to stop them.

Many of the victims of the ​epidemic have been healthcare ​workers, including those ⁠who caught the virus before the outbreak was declared in mid-May. Other healthcare workers lack equipment such as boots, gloves ​and waterproof overalls to protect themselves from Ebola, which is ​transmitted ⁠through bodily fluids.

Healthcare workers in the worst-hit province of Ituri went on strike recently, complaining of delays in salary payments.

“Most of the health workers restarted work as ⁠of ​yesterday. There are still a few groups who ​are dissatisfied," said Ancia, adding that some of those still on strike had been controlling transmission ​in a displacement camp.