Rising food prices are tightening the squeeze on populations already struggling to buy adequate food, demanding radical reform of the global food system, Oxfam has warned.

By 2030, the average cost of key crops could increase by between 120% and 180%, the charity forecasts.

It is the acceleration of a trend which has already seen food prices double in the last 20 years.

Half of the rise to come will be caused by climate change, Oxfam predicts.

It calls on world leaders to improve regulation of food markets and invest in a global climate fund.

"The food system must be overhauled if we are to overcome the increasingly pressing challenges of climate change, spiralling food prices and the scarcity of land, water and energy," said Barbara Stocking, Oxfam's chief executive.