The World Health Organization said on Thursday it was still trying to slow the rate of new infections but had "reasonable confidence" that the Ebola virus plaguing three West African countries had not spread into neighboring states.

Asked whether countries such as Guinea Bissau, Mali and Cote d'Ivoire might have cases of the disease crossing their borders without knowing about or reporting them, WHO assistant director-general Keiji Fukuda said he considered that unlikely.

"I think that there is reasonable confidence right now that we are not seeing widespread transmission of Ebola into the neighboring countries," Fukuda told a news briefing in Geneva.