Secretary-General Ban Ki-moon warned Tuesday that as long as there is one Ebola case in West Africa "all countries are at risk" and urged all nations to support the final battles to wipe out the deadly disease in Sierra Leone and Guinea.

"We are on the home stretch now and what happens now is critical," the UN chief told a General Assembly meeting on efforts to end the Ebola epidemic that has killed over 11,100 people mainly in Liberia, Sierra Leone and Guinea since it was first reported in March 2014.

Liberia, once the worst affected country, is now Ebola free, but Ban warned that in Sierra Leone and Guinea "the battle has not yet been won" and "any lapse in vigilance could allow the virus to spread."

Dr. David Nabarro, the UN Ebola chief, told the assembly that the priority is to ensure the outbreak ends as soon as possible "which will take several weeks and may take a number of months."

"But everybody should be ready in case the disease recurs and needs to be controlled, especially in the coming 12 months," he said.

The secretary-general said UN agencies who will be taking over responsibility for tackling Ebola as the UN Mission for Ebola Emergency Response known as UNMEER scales down "will need considerable resources to go the distance and support recovery" in the three hardest-hit countries.

UNMEER's acting chief Peter Jan Graaff said UNMEER's Mali office closed on March 31, its Liberia office already handed over operations to the UN country team and the Sierra Leone office is expected to end operations by the end of June.

"UNMEER could complete its transition by July 31 and be closed by the end of August," he said.

If the situation deteriorates, however, Graaff said, the timeline could be changed "to ensure that the UN's political leverage and convening power is maintained."

Ban said he will convene an International Ebola Recovery Conference in New York on July 10 to mobilize resources to start early recovery in Liberia, Sierra Leone and Guinea.

"We must also translate lessons learned from this Ebola outbreak into stronger national and international systems to prevent and respond to health crises," he said.

Last week, the World Health Organization's decision-making body examined how the response could have been improved to reduce suffering, deaths and other consequences including serious economic damage. Ban has also commissioned a high-level panel on improving the Global Response to Health Crises led by Tanzania's President Jakaya Kikwete.