The United Nations cautioned over rice prices following those of other cereals higher as, it slashed its forecast for the Indian harvest by 7.8m tonnes and highlighted the threat of export curbs.
In Chicago, rough rice futures for September hit a nine-month high of $16.09 per hundredweight in Chicago before easing in late deals.
The UN food agency, the Food and Agriculture Organisation, said that "much uncertainty prevails" over the future of global rice prices, despite their "surprising" stability so far in the face of the rally in corn and wheat markets.
Values have been depressed by a bumper world 2011-12 harvest and the prospect for many producing countries of a strong follow-on crop too, leaving world stocks set to hit a comfortable 34% of use next year.
The stocks-to-use ratio, as a measure of the level of competition needed among buyers to secure supplies, is a much-watched guide to prices.
Inventories are particularly high in Thailand, thanks to a government farm-support programme, which has raised the prospect of a large sell-down in stocks to make space for the next harvest, in October.
However, the FAO warned that Thai dynamics "must be weighed against India's possible consideration of a reinstatement of export restrictions" following the hit to its harvest hopes from a weak monsoon.
Separately, US Department of Agriculture staff in New Delhi cut their estimates for India's cotton crop following the weak start to the monsoon, which official meteorologists admitted last week will prove "deficient" for the first time since the drought year of 2009-10.
The FAO slashed its forecast for India's rice crop, the world's second-biggest after China's, by 9.8m tonnes to 147.7m tonnes, equivalent to 98.5m tonnes on a milled basis, and representing a 6% decline year on year.
Inventories were seen dropping 10% to 22.8m tonnes over 2012-13.
US broker Benson Quinn Commodities said: "The trade is also paying close attention to a monsoon season in India that has been disappointing to this point," flagging the rise in Chicago rough rice futures to multi-month highs.
The importance of rice as a food staple in many countries renders them particularly vulnerable to political interference for fears of a squeeze, and fuelled the jump in prices in 2007-08.
Government action then included a ban on exports of non-basmati rice by India, besides a ban on commercial sales by Vietnam, and penalties for hoarding introduced by Thailand.
In fact, world inventories grew over 2007-08, and indeed are expected to increase in 2012-13 for an eighteen successive season on FAO estimates.
Indian politicians are particularly active in export markets, temporarily banning cotton shipments earlier this year and keeping close control over sugar sales overseas, making the impact of the monsoon a sensitive factor for many markets.
'Trickle down' risk
Extra upward pressure on rice prices may come from spillover from world corn and wheat markets, where values have been sent soaring by poor prospects for harvests in the US and much of the former Soviet Union.
"Developments in other cereal markets will need to be closely monitored," the FAO said.
The rally in "other cereal markets may eventually trickle down to affect the rice economy".
The FAO cut its estimate for the world rice harvest in 2012-13 by 7.8m tonnes to 724.5m tonnes, or 483.1m tonnes on a milled basis, although this would still come in ahead of consumption.