Geneva - Nearly $13bn in humanitarian aid will be needed this year - a third of it just for Syria - to help 73 million people suffering around the world, the UN's top humanitarian official said on Wednesday.
But that's just an estimate, midway through 2013, of what will be needed in what is turning out to be an "unprecedented" challenge, said Valerie Amos, the UN undersecretary-general for humanitarian affairs and emergency relief.
The likelihood is that as much as a third of what's needed won't be raised, according to the UN's own figures.
Over the past five years, the United Nations has only been able to scrounge up between 63% and 72% of what it says is required to feed, house and provide other help to the millions of people trying to survive often desperate conditions.
Amos told reporters: "Halfway through the year, we know that 73 million people need humanitarian assistance".
"The increase is largely due to the exploding crisis in Syria and the neighbouring region, but also because situations have worsened in other countries like the Central African Republic and Mali."
Amos, a British baroness who heads the UN office for the co-ordination of humanitarian affairs, said Syria alone requires at least $4.4bn in aid for the 6.8 million people who are suffering inside the war-torn country and the 5.3 million refugees or others who are affected by the conflict in border nations.
So far, a little more than $5 billion, or about 40% of what is needed around the world, has been raised for humanitarian aid by mid-year, said Amos, who conceded that she had "no idea" how to get the rest.
The money is meant to pay for the work of 620 UN and affiliated aid agencies.
"In a normal year, that would be a huge statement to the commitment to humanitarian action," she said of the $5.1bn raised so far that has gone to people in 24 countries, including Syria, Niger, Sudan and Afghanistan, but said: "This is an extraordinary year."