"It remains a deadly and a massive epidemic. There are some areas of progress, but nonetheless, in other areas, we continue to see growth in cases," Julien Harneis, the UN special Ebola co-ordinator, told a Geneva media briefing on Tuesday.
The outbreak in the Democratic Republic of the Congo is the second most lethal on record, behind one in West Africa that lasted from 2014 to 2016.
Asked about reports that the epidemic had reached a turning point, the World Health Organisation's Olivier le Polain said: "It's too early to confidently say we have passed a peak.
"It will take many, many months to get this outbreak under control fully, and it will require significant support."
On Saturday, Congo Health Minister Samuel Roger Kamba said there were "encouraging signs" in the fight against Ebola since "the peak reached in mid-August", and that transmission "has been gradually slowing down".
He said daily new cases had dropped from about 120 "at the peak of the epidemic" to about 80, and that 10 of the 62 affected health zones had recorded no new cases for more than 22 days.
"To me, these figures are a positive sign. They demonstrate that the efforts deployed on the ground are yielding results and that our response strategy is beginning to bend the transmission curve," he said.
"However, we must remain fully mobilised. While these results are encouraging, they must not lead us to lower our guard."
There have been 7258 confirmed cases and 3510 deaths across seven provinces, according to government figures published on Tuesday.
UN officials on Tuesday said they were seeing progress in parts of Ituri, which remains the most affected province, and that in some areas the outbreak is now "under control".
But they said cases were still rising fast in North Kivu, particularly in the city of Butembo.
"It's such a vast epidemic that it's difficult to talk about one epidemic, but there's rather many different locations," Harneis said.
"We know from past experience that an epidemic can show early signs of improvement and then pick up again quite quickly," Le Polain, head of epidemiology and analytics for response at the WHO Health Emergencies Programme, said.
Aid workers say more needs to be done to curb transmission in North Kivu.
"The situation in North Kivu, with its very complex security situation, high population density and mobility, is alarming," said Thomas Paerisch, a public health specialist recently deployed to Democratic Republic of Congo with Medecins Sans Frontieres.
North Kivu is the second most affected province, with a cumulative number of 1269 confirmed cases, including 555 reported in the past 21 days, as of September 12.
