ROME – The United Nations food agency on Friday warned that record-high prices for basic commodities are generating unrest around the world and helped topple the Tunisian president last month.

"Not only is there a risk, but there have already been riots in some parts of the world because of rising prices," Jacques Diouf, head of the UN's Food and Agriculture Organisation (FAO), told reporters in Rome.

"Some governments have found themselves in difficult situations and there is even one that has fallen," he said -- a reference to the ousting of Tunisia's Zine El Abidine Ben Ali in a popular revolt on January 14.

The FAO on Thursday said food prices have reached their highest level since the UN agency began measuring them in 1990.

The FAO's index measuring monthly variations for a variety of staples rose 3.4 percent from December 2010 to reach 231 points.

France, which has promised to stamp out food price volatility as the current head of the G20 group of leading world economies, warned of "hunger riots".

"There is a real risk of hunger riots," French Agriculture Minister Bruno Le Maire said at a joint press conference with Diouf.

Le Maire called for "structural measures" to avoid spikes in food prices, including greater transparency over production and stocks.

He said that G20 countries should agree on a system of food stocks that can be released for parts of the world that are most at risk.

"Speculation on hunger in the world is economically dangerous and morally unacceptable," he said, referring to widespread criticism of the role played by financial speculators on global commodity markets.

A previous sharp rise in food prices in 2007 and 2008 triggered food riots in a number of African countries, as well as in Haiti and the Philippines.

The average for the FAO's Food Price Index in 2008 was 200 points.