The head of the World Health Organization (WHO), Margaret Chan, warned the spiralling tropical epidemic demanded a stronger, faster response from the international community.
"In the three hardest-hit countries, the number is moving faster than the capacity to manage them," she told a news conference in Geneva.
The alarm call came as the UN vowed its peacekeeping force in Liberia - one of the worst-affected countries along with Guinea and Sierra Leone - would ‘stay the course’ against Ebola.
"As of 12 September, we are at 4,784 cases and more than 2,400 deaths," a jump of around 100 since the WHO's previous toll on Tuesday, the UN health chief said.
She did not specify if the figures also included Nigeria, which has reported 18 cases, seven fatal, since the deadliest Ebola outbreak on record began in Guinea at the start of the year.
Transmitted through bodily fluids, the tropical virus leads to haemorrhagic fever and - in over half of cases - death. There is no specific treatment regime and no licensed vaccine.
Another 500 foreign health professionals and around 1,000 local doctors and nurses are needed to stop its deadly surge through West Africa, the UN health agency said.
"The thing we need most of all is people," Chan told a joint news conference with Cuban Health Minister Roberto Morales Ojeda.
Cuba pledged to send 165 doctors and nurses to Sierra Leone, where more than 500 people have so far died – a commitment Chan hailed as the ‘largest’ so far.
Starting the first week of October, the 62 doctors and 103 nurses will remain for six months in Sierra Leone, Ojeda said.
All have "previously participated in post-catastrophe situations," and all volunteered for the mission, he said, adding that some were already in the country.
In neighbouring Liberia, Chan said that there is not a single bed left to treat Ebola patients.
The UN said that its peacekeepers will not abandon the country, whose war-ravaged health services were on the slow road to recovery when the Ebola outbreak began.
"We are here to stay the course and to help the people of Liberia and its neighbours to get through this terrible crisis," UN peacekeeping chief Herve Ladsous said.

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