(New throughout; updates prices, adds quotes, changes byline, changes dateline from previous PARIS/SINGAPORE)
CHICAGO, Sept 21 (Reuters) - U.S. benchmark soybean futures fell below $13 a bushel on Thursday for the first time in a month while corn and wheat futures held near multi-year lows on downbeat weekly export sales, an expanding U.S. harvest and economic worries, analysts said.
As of 12:30 p.m. CDT (1730 GMT), Chicago Board of Trade November soybeans were down 23-3/4 cents at $12.96-1/4 a bushel after hitting $12.94-1/4, the contract's lowest since Aug. 8.
CBOT December corn was down 7 cents at $4.75-1/4 a bushel, while December wheat was down 9 cents at $5.79-3/4.
Soybean futures extended early declines after the U.S. Department of Agriculture (USDA) reported U.S. soy export sales in the week to Sept. 14 at 434,100 metric tons, below a range of trade expectations. Weekly corn sales of 566,900 tons fell near the low end of expectations.
Confirmation by the USDA of daily private sales of 137,160 tons of U.S. corn to Mexico did little to lift the mood.
Export demand for U.S. grains has lagged amid plentiful supplies of both crops from Brazil, a firm dollar and low water on the Mississippi River that has slowed the movement of barges to Gulf export terminals.
The export woes have overshadowed uncertainty about the size of drought-hit U.S. crops as combines start to roll in the heart of the Midwest.
"My bias is still that we will see both USDA's corn and soybean yields slide lower going forward, but that really doesn't matter to the market right now when export demand remains so weak," Arlan Suderman, chief commodities economist at StoneX, wrote in a client note.
Meanwhile the dollar hit a six-month high after the U.S. Federal Reserve signalled policy would remain restrictive for longer, further clouding U.S. grain export prospects.
"The Fed's hawkish 'higher for longer' interest rate projections are negatively impacting risk assets and commodity markets via the strong dollar," Peak Trading Research wrote in a note.
In other news, the International Grains Council (IGC) in a monthly update raised its 2023/24 global corn crop forecast by 1 million metric tons to 1.222 billion tons.
However, the IGC trimmed its 2023/24 world wheat crop outlook by 1 million metric tons to 783 million, with downgrades for Australia, Canada and Argentina.
Australia's crop has struggled with hot and dry weather this month at a crucial period for crop development.
(Reporting by Julie Ingwersen in Chicago; Additional reporting by Gus Trompiz in Paris, Naveen Thukral in Singapore and Peter Hobson in Canberra; Editing by Rashmi Aich, Shilpi Majumdar and Jan Harvey)
