US president Barack Obama has branded the deadly Ebola outbreak "a threat to global security' and announced that the US will play a larger role in combatting the virus.

"The world is looking to the United States," Mr Obama said, but added the outbreak required a "global response".

"In West Africa, Ebola is now an epidemic, of the likes that we have not seen before. It's spiralling out of control; it is getting worse; it's spreading faster and exponentially," Obama said.

"Today thousands of people in West Africa are infected. That number could rapidly grow to tens of thousands. And if the outbreak is not stopped now we could be looking at hundreds of thousands of people infected with profound political and economic and security implications for all of us."

"This is an epidemic that is not just a threat to regional security. It's a potential threat to global security if these countries break down, if their economies break down, if people panic," the president addd. "That has profound affects on all of us even if we are not directly contracting the disease."

The US president spoke from the Centers for Disease Control and Prevention (CDC) in Atlanta, where he received a briefing on the outbreak and met with scientists, doctors and health care workers battling the spread of the virus.

Meanwhile, more than $1bn (£618m) is needed to fight the Ebola epidemic, which UN officials have called a health crisis "unparalleled in modern times".

The spread of the disease means the funds needed to fight the outbreak have increased ten times in the past month, the UN's Ebola co-ordinator said in a BBC report.

Ebola has killed 2,461 people this year, according to figures from the World Health Organization.

There has been intense criticism of the slow international response to the epidemic, with pharmaceutical companies in the firing line.