DUBAI, United Arab Emirates (AP) - The U.N.'s top humanitarian official warns that continuing rising food prices could cause unrest and political instability worldwide.

John Holmes, the undersecretary general for humanitarian affairs and emergency relief coordinator, has told a humanitarian aid conference in Dubai that rising food prices are already exacerbating emergencies around the world.

"The security implications (of food crisis) should also not be underestimated as food riots are already being reported across the globe," he said.

"Current food price trends are likely to increase sharply both the incidence and depth of food insecurity," he said, noting a 40 percent average rise worldwide since mid-2007.