GENEVA (AFP) - The rate of new Ebola infections appears to be slowing in hard-hit Liberia, but the crisis is far from over, the World Health Organisation said on Wednesday.

"It appears that the trend is real in Liberia and there may indeed be a slowing of the epidemic there," WHO assistant director-general Bruce Aylward told reporters in Geneva.

"There is increasing evidence that these countries can get on top of this," he said.

Aylward added, though, that he was "terrified that the information will be misinterpreted and that people will begin to think Ebola is under control."

"That is like thinking your pet tiger is under control," he warned, pointing out that the deadly outbreak had seemed to slow previously only to come back with more gusto.

Later on Wednesday, the WHO is set to publish the latest death toll from the Ebola outbreak that has been ravaging west Africa, with the number of deaths expected to pass the 5,000 mark. Guinea, Liberia and Sierra Leone have been most affected.

Washington meanwhile ordered a 21-day quarantine for all US troops returning from west Africa, calling it a "prudent" measure to prevent the spread of the virus.

Aylward said that the number of cases had soared to 13,703 - up from just over the 10,000 WHO reported on Saturday - but he stressed that the increase was mainly due to previously unreported cases being added to the statistics.

Despite the panicked response seen in the United States especially over the handful of cases there, he stressed that virtually all cases - 13,676 of them - were to be found in the three west African countries at the heart of the outbreak.

Liberia alone counted 6,535 cases, Sierra Leone had 5,235 and Guinea, where the outbreak began late last year, counted 1,906 cases, he said.

Neighbouring Mali, where a two-year-old girl died from Ebola following a 1,000km bus ride from Guinea, had not yet detected any new infections, he said.

Aylward said data from a range of different sources - including from funeral directors and from treatment centres reporting lower Ebola patient admission rates - indicated a "downward trend" across much of Liberia.

A number of beds at Ebola treatment centres in the country were now empty, he said.

A rapid scaling up of information to the community about the deadly virus, contact tracing and implementation of safe burial practices had likely contributed to the positive trend seen in Liberia, he explained.

Aylward's cautious optimism on the situation in Liberia came a day after US President Barack Obama and the Red Cross offered hope that progress was being made in the battle against the killer virus.

The Red Cross said its workers were picking up little more than a third of the late September peak of more than 300 bodies a week in and around Monrovia - an indication, it said, that the outbreak was retreating.

And Obama insisted the disease "will be defeated".

He said Washington would remain "vigilant," but stressed that science, not fear, should guide the response to the virus.

There has been growing condemnation of Washington's rush to quarantine people have come in contact with those suffering from the Ebola, amid fears such strict measures could dissuade much-needed health-care workers and others from travelling to the affected region.

UN chief Ban Ki-moon on Monday criticised the enforced quarantine of an American nurse who had returned to the US from Sierra Leone. He said the only way to stop the epidemic was "at its source".

Nonetheless, Pentagon chief Chuck Hagel on Wednesday ordered a three-week quarantine for all US troops returning from west Africa.

"The secretary believes these initial steps are prudent," his spokesman Rear-Admiral John Kirby said in a statement.

The quarantine was introduced even though officials say the soldiers will be focused on building medical clinics or training and will have no contact with those infected with the virus.

Hagel said the measure was adopted partly because military families urged the quarantine.

Earlier, a US decision to put a dozen American soldiers returning from Liberia into quarantine for Ebola at their base near Venice rather than in the United States sparked controversy in Italy.

"They shouldn't have been sent here, they should do their quarantine for Ebola at home," said the president of the region's assembly, Luca Zaia.

For the WHO, the main priority remains ramping up the number of treatment centres in west Africa, with the aim of bringing the total number of centres to 56, with 4,700 beds.

"We are making real progress," Aylward said, pointing out that 15 of the centres were already fully functional.

But he added that a lack of medical teams remained a key challenge.