ROME, June 5 -- World food prices dropped for the 13th time in 14 months in May, reaching their lowest levels in nearly six years, almost 21 percent below already-low levels from a year ago, the United Nations Food and Agriculture Organization (FAO) said in a new report.

The overall FAO World Food Price Index was 166.8 points, 1.4 percent below its level in April. The last time the index dipped that low was in September 2009.

All indications were that prices would continue to fall: a new FAO publication predicted rice supplies would be 1.3 percent higher this year than in 2014, though the publication's authors said cereal harvests over the next several months could have an impact on prices if there are problems.

In May, the sub index of cereals and grains, the largest component in the overall index, was 3.8 percent lower, setting the pace for the overall drop. Prices for dairy products fell 2.9 percent compared to April, and meat prices were 1.0 percent lower, nearly reversing the slight rise in prices between March and April.

Two components saw prices rise, though not by enough to derail the overall fall in prices: sugars rose 2.0 percent, due to short-term problems in Brazil, and oils and fats rose 2.6 percent, partly due to worries that the El Nino weather phenomenon could impact production in southeast Asia.

The next installment of the FAO index, which is based on a basket of 55 goods and 73 price quotations in five major food commodity groups, will be released July 9.