More than $1bn is needed to fight the West Africa Ebola outbreak - a tenfold increase in the past month, the UN's Ebola coordinator has said, according to BBC News.

David Nabarro made the announcement as the World Health Organization (WHO) described the health crisis as "unparalleled in modern times".

It has killed 2,461 people this year, half of the 4,985 infected by the virus, the global health body said.

There has been criticism of the slow international response to the epidemic.

Later, the US president is to announce plans to send 3,000 troops to Liberia, one of countries worst-affected by the outbreak, to help fight the virus.