US President Barack Obama says all but 100 of the US troops stationed in Liberia to fight the spread of Ebola will pull out by the end of April.

There were 2,800 US troops in West Africa at the height of the epidemic.

Liberian President Ellen Sirleaf Johnson has told the BBC she is "very optimistic that Ebola can be beaten".

She warned, however, that "there is a danger of the disease coming back", and said Liberia needs "a health system that can work".

President Obama's announcement of a near-total withdrawal of US troops from Liberia follows the news that the number of new Ebola cases has risen for the second consecutive week, ending a period of encouraging declines.

The World Health Organization (WHO) says Sierra Leone has registered 76 of the 144 new cases, while Guinea has registered 65 and Liberia three.

'Saddened'

President Johnson told BBC World Service's Newshour that although there had been a "delay" in other countries offering help to fight the virus, when assistance did arrive, "it came so fully and so effectively".

"We can say that success is also owed to the international community," she added.

"At one point I was saddened that the response was so slow and at that point ineffective, but I can't be angry, we have to take responsibility."

She said the poor state of Liberia's healthcare system had exacerbated the problem of trying to contain the spread of the virus initially, and called on the world to "work with us" in improving the system.

"Our resources are scarce, we did not have enough trained medical personnel, we did not have enough facilities in the hospitals and clinics, but under the circumstances we did what we could," she said.

The president said co-operation with Liberia's neighbours was required to contain the virus, due to the country's "porous borders that are very long [and] unprotected".

Last week, the country had just a handful of confirmed Ebola cases, down from about 300 a week in August and September 2014.

Announcing the pullout of US troops, in the presence of six of the eight US survivors of the deadly virus, Mr Obama said the move represented the transition into "the next phase of the fight".

Ebola deaths

Mr Obama said that as the military contingent in Liberia was reduced, his government was "expanding our civilian response".

The president said around 10,000 "civilian responders" would stay in West Africa to fight the virus.

"Every case is an ember that if not contained can light a new fire. So we're shifting our focus from fighting the epidemic to now extinguishing it," he said.

Around 1,500 US soldiers have already returned from the region, with all troops leaving West Africa forced to undergo a 21-day quarantine period in order to minimise the risk of contagion.

Almost 23,000 people have been infected with Ebola since its outbreak in Guinea in December 2013, and more than 9,000 people have died.

The WHO has said that the increase in new cases highlights the "considerable challenges" that must still be overcome to end the outbreak.

"Despite improvements in case finding and management, burial practices, and community engagement, the decline in case incidence has stalled," the UN health agency said in a statement.