GRAINS-Chicago corn falls on profit-taking from three-year highs

BEIJING, Sept 3 (Reuters) - Chicago Board of Trade corn futures fell on Thursday as traders took profit after prices set a three-year high, but uncertainty over the conflict in the Black Sea grain-exporting region underpinned the market, traders said.

Wheat and soybeans gained.

The most-traded corn contract on the Chicago Board of Trade (CBOT) Cv1 dropped 0.3% to $5.42 a bushel by 0245 GMT. CBOT Wv1 was up 0.2% at $7.75 a bushel, while soybeans Sv1 rose 0.4% to $13.15 a bushel.

Escalating Black Sea tensions have cast uncertainty over global grain availability. Attacks over the last months have halted almost all grain shipments through ports in the Black Sea and the Sea of Azov, which used to account for 70% of all Russian grain exports.

Russia's Deputy Foreign Minister Alexander Grushko told reporters on Wednesday that the country sees no grounds for the Black Sea grain deal to resume, as Russia and Ukraine continue to attack each other's grain export facilities.

Ukraine's largest farm union UAC warned exporters on Wednesday not to expect deepwater ports to resume operations soon and to rely on alternatives.

Russia attacked Ukraine's port infrastructure and a border crossing with Romania in the southern Black Sea region of Odesa overnight, Ukrainian officials said on Tuesday.

Traders remain on edge over the risks of a prolonged interruption to Russian and Ukrainian grain exports from the Black Sea region.

Ahead of Thursday's weekly USDA export sales report, traders expected the government to report net export sales of U.S. old-crop corn in the week ended August 27 at up to 200,000 metric tons and new-crop sales of up to 1.6 million tons. They also expected up to 200,000 metric tons of U.S. old-crop soybean net export sales and new-crop sales of up to 2.5 million tons.