(New throughout; updates prices, adds quotes; changes byline, dateline, previous LONDON) CHICAGO, May 31 (Reuters) - U.S. soybean futures fell Thursday on worries about global trade tensions, analysts said, while wheat and corn firmed on bargain-buying and fears of tightening global supplies. As of 12:23 p.m. CDT (1723 GMT), Chicago Board of Trade July soybeans were down 3-1/2 cents at $10.19-1/2 per bushel. July wheat was up 4-1/2 cents at $5.26-1/2 a bushel and July corn was up 1-1/2 cents at $3.95. Soybean futures turned lower after the United States said it would impose tariffs on aluminum and steel imports from Canada, Mexico and the European Union, reigniting fears of a global trade war. The move came days ahead of a visit by U.S. Commerce Secretary Wilbur Ross to China, the world's biggest soy importer. Ross is expected to try to get China to agree to firm numbers to buy more U.S. goods during a June 2-4 visit to the Chinese capital. "It's the start of these Chinese negotiations that everybody's worried about. It looks like the tariffs on steel and aluminum on our partners are threatening enough that the market is unsure what will happen in China," said Dan Basse, president of AgResource Co in Chicago. The CBOT July soybean contract at times dipped below its 200-day moving average near $10.17 as traders adjusted positions on the last day of the month. The contract was poised to fall about 29 cents, or 2.7 percent, for May. Corn clung to modest gains despite the trade tensions with Mexico, a top buyer of U.S. corn. Mexico responded to U.S. steel and aluminum tariffs by imposing wide-ranging "equivalent" measures on farm and industrial products, including pork, apples, grapes and cheeses. Corn futures found support from bargain buying a day after the July contract hit its lowest level in a month, and uncertainty about U.S. crop weather after an unusually warm May. "The weather has actually gotten more threatening over the last 2 or 3 days, Basse said, adding that U.S. corn and soy crops "look good today, but that is not a barometer of where they will finish." Wheat firmed, with the CBOT July contract rebounding from a one-week low of $5.15-1/4 a bushel on technical buying and worries about dryness in the Black Sea region, including Russia and Ukraine. Russia is expected to reduce its 2018 crop of winter wheat and rye by around 10 percent from a year ago due to dry weather, a state weather forecaster said.
CBOT prices as of 12:24 p.m. CDT (1724 GMT):
Last Net Pct Volume
CBOT wheat WN8 526.25 4.25 0.8 67712 CBOT corn CN8 395.00 1.50 0.4 148993 CBOT soybeans SN8 1019.50 -3.50 -0.3 80491 CBOT soymeal SMN8 375.70 -1.20 -0.3 27374 CBOT soyoil BON8 31.12 -0.36 -1.1 45190
NOTE: CBOT July wheat, corn and soybeans shown in cents per bushel, soymeal in dollars per short ton and soyoil in cents per lb.
(Additional reporting by Nigel Hunt and Naveen Thukral; Editing