LONDON, June 7 (Reuters) - The United Nations world food price index rose for a third consecutive month in May, as higher cereals and dairy product prices outweighed decreases in prices for sugar and vegetable oils.

The UN Food and Agriculture Organization's (FAO) price index, which tracks the most globally traded food commodities, averaged 120.4 points in May, up 0.9% from its revised April level, the agency said on Friday. (Reporting by Maytaal Angel; Editing by Jan Harvey)