World food prices edged up in September after a sharp fall in August, staying much lower than a year ago but showing signs of stabilizing, the United Nations food agency said on Thursday.

The Food and Agriculture Organization's (FAO) food price index, which measures monthly changes for a basket of cereals, oilseeds, dairy, meat and sugar, averaged 156.3 points in September, up one point from August.

The index has been sliding for most of the past 18 months, partly thanks to rising global supply, and is still hovering near an almost six-year low hit in August.

Prices in September were 18.9 percent below a year ago, but firming energy prices and a stronger U.S. dollar could support future prices, said FAO senior economist Abdolreza Abbassian.

"This little increase that we saw last month in the food price index may be an indication that we are reaching a bottom, and that the prices, although they are not going to spike anywhere, are also not going to collapse any further," he said.

"It looks like the so-called super-cycle has firmly ended and we are in a more normal situation," Abbassian said, although weather patterns such as El Nino could create price spikes.

September's rise was led by firming values for sugar and dairy, which rose 3.2 percent and 5 percent respectively. Other commodities remained close to or below the August levels.

FAO cut its 2015 world cereal output forecast to 2.534 billion tonnes, from a previous figure of 2.540 billion tonnes, due to lower production prospects for coarse grains and rice.

But wheat harvests are on track for a record year, thanks to higher output from China and the European Union, and FAO's estimates could be revised up further on the back of recent figures published for production in Canada, Abbassian said.

However, lower prices have not stimulated trade and the global value of imported foodstuffs is set to plummet to a 5-year low of $1.09 trillion in 2015, FAO said in a separate market outlook published on Thursday.

"A lot of importing countries for a variety of reasons do not see any rush to go to the market and buy their food, either because they have better supplies or home, or in some instances ... demand is weaker," Abbassian said.