UN World Food Programme (WFP) director Ertharin Cousin said that it is being forced to scale back projects in a number of countries as it confronts a £612 million funding shortfall.

The organisation's costs are mounting for missions such as Syria, she said.

Ms Cousin is in Australia as part of a tour to drum up support for the agency among donor nations and the private sector to help feed the world's hungry.

"We have about $1bn (£612m) more in identified need in 2014 than we have projected revenues," she said.

And she warned that rations were being slashed across programmes in nations including Haiti, Niger, Mali and Kenya, where refugees in the sprawling Dadaab camp saw 10 per cent cuts in December and a further 10 per cent last month.

Ms Cousin said it was "because we lack enough money to feed everybody a full meal."

Costs are mounting for operations in Syria, where the WFP aims to reach 4.25 million people at a cost of £25m a week.

"Donors target their funds and when donors target their funds it means that they cut their funds in other places," Ms Cousin said.

She added that there were "hundreds of thousands of people in Syria that we can't reach on an ongoing basis" but stressed that where aid was getting through "it means that we're making a difference."

Costly aerial operations were also being considered for the war-torn Central African Republic, where Ms Cousin said over 50 WFP lorries were currently held at the border awaiting armed escort and 800,000 internally displaced people needed food.

"We are planning to fly food next week from Cameroon into Bangui city," she said.

"Again it will cost us more and we will have fewer people that we can serve, but if we don't start next week we won't have enough food left to feed people inside Central African Republic anymore."