SINGAPORE, May 18 (Reuters) - Chicago wheat futures lost more ground on Thursday, as an extension of a deal to allow war-ravaged Ukraine to continue exporting grains eased concerns over world supplies.

Corn slid to trade near an 18-month low hit in the previous session after China cancelled purchases of U.S. cargoes and as favourable weather helped newly planted crops in the Midwest.

FUNDAMENTALS

* The most-active wheat contract of the Chicago Board of Trade (CBOT) slid 0.8% to $6.20-1/4 a bushel, as of 0019 GMT, extending losses for a third session. Corn fell 0.8% to $5.57 a bushel and soybeans gave up 0.3% to $13.32-1/2 a bushel.

* The Ukraine Black Sea grain deal has been extended for two more months, in what U.N. Secretary-General Antonio Guterres hailed as "good news for the world," a day before Russia could have quit the pact over obstacles to its grain and fertiliser exports.

* Corn futures faced pressure after the U.S. Department of Agriculture said private exporters cancelled purchases of 272,000 tonnes of old-crop U.S. corn earmarked for China, the fourth such cancellation in the last month.

* Meanwhile, the 2023 U.S. corn and soybean crops are off to a solid start, with a faster-than-average planting pace and mostly crop-friendly weather pointing towards rising supplies.

* Commodity funds were net sellers of CBOT wheat, soybean, corn, soyoil and soymeal futures contracts on Wednesday, traders said.

MARKET NEWS

* Wall Street rallied to a higher close on Wednesday, gathering momentum throughout the afternoon trading, and the dollar touched a six-week high as regional banks surged and negotiations in Washington over raising the debt ceiling progressed.

DATA/EVENTS (GMT) 1230 US Initial Jobless Clm Weekly 1230 US Philly Fed Business Indx May 1400 US Existing Home Sales April (Reporting by Naveen Thukral; Editing by Subhranshu Sahu)