WASHINGTON — President Obama heralded a “new phase in the fight” against Ebola on Wednesday and said progress against the outbreak in West Africa will allow the U.S. to withdraw nearly all American troops sent to Liberia last fall.

He cautioned the mission was not over, and he set an ambitious goal of eliminating the disease.

“We have risen to the challenge,” he said at the White House. “Our focus now is getting to zero.”

Obama said only 100 of the 2,800 troops sent to Liberia will remain there after April 30. About 1,500 have returned home. Those staying will work with Liberia’s military, regional partners and U.S. civilians.

Obama’s upbeat announcement, made with military responders and Ebola survivors at his side, was a significant turnabout from last year when the White House’s initial response to the outbreak was criticized as inept and too slow.

Back then, Obama resisted calls to impose a travel ban and was forced to cancel midterm campaign appearances to stay in Washington and focus on Ebola, particularly after health workers contracted the virus at a Texas hospital while treating a man who was infected in Africa.

“People were understandably afraid,” Obama said Wednesday. “Some stoked those fears.”

The outbreak has killed more than 9,100 people.