BEIJING, June 23 (Reuters) - Chicago grain futures rebounded on Tuesday after two straight sessions of losses, supported by firmer crude oil prices amid tempered optimism over U.S.-Iran peace talks.

Wheat gained additional support after U.S. winter wheat ratings came in below expectations due to a drought.

FUNDAMENTALS

* The most-active soybean contract on the Chicago Board of Trade (CBOT) Sv1 was up 0.31% at $11.45 a bushel, as of 0102 GMT, while corn Cv1 rose 0.24% to $4.12-1/2 a bushel. Wheat Wv1 climbed 0.37% to $6.09-3/4 a bushel.

* The U.S. Department of Agriculture left its ratings of U.S. corn and soy crops unchanged from last week in its weekly crop progress report on Monday, with corn in 68% and soybeans in 66% good-to-excellent condition.

* Winter wheat ratings, however, dropped 1 percentage point from last week to 26% good-to-excellent, below the average analyst estimate of 27%, after a severe drought in the U.S. Plains wheat belt decimated the crop.

* Soybeans remain under pressure from ample global supplies. In Brazil, the soybean planting area for the 2026/27 crop year is forecast to reach a record 49.006 million hectares, a 0.9% increase from the previous cycle, consultancy AgRural said on Monday in its first forecast.

* In wheat markets, advancing U.S. harvest activity and favourable crop prospects in Russia and Ukraine weighed on prices.

* Firmer crude oil prices are likely to support agricultural markets, with increasing use of soybeans and corn in making biofuels.

* Commodity funds were net sellers of CBOT corn and soybean futures, traders said on Monday. CBOT/FUNDS

MARKET NEWS

* The dollar climbed on Monday as the initial round of U.S.-Iran talks buoyed optimism for a peace deal while the pound was higher in choppy trading after British Prime Minister Keir Starmer announced that he would resign. FRX/

DATA/EVENTS (GMT)

0645 France Business Climate Mfg, Overall Jun

0715 France S&P MFG, Services, Composite Flash PMI Jun

0730 Germany S&P MFG, Services, Composite Flash PMI Jun

0800 EU S&P Mfg, Services, Composite Flash PMI Jun

0830 UK Flash Composite, Manufacturing, Services PMI Jun

1345 US S&P Global Mfg, Svcs, Comp PMI Flash Jun