Suicide bombing was aimed at African Union troops in Somalia.
Vaccinated monkeys have developed "long-term" immunity, raising prospect of successful human trials.
Group says 40% of the dead succumbed in the past three weeks.
Rice and maize production will be particularly affected during harvest season, U.N. group says.
W.H.O. reports more than 20,000 could be infected before outbreak can be brought under control.
Helicopter said to have been shot down.
Riot police training academy said to be overrun by militants.
Police in the capital fired live rounds and tear gas to disperse stone-throwing crowd.
Since March, the virus has infected at least 5,000 people, killed 2,630.
Two Islamist fighters were killed in clashes with security forces.
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