CHICAGO, Dec 22 (Reuters) - Chicago Board of Trade soybean and corn futures extended a rally to new multi-month peaks on Wednesday as dry weather in some South American growing belts stoked supply concerns. Wheat futures rose for a fifth straight session, tracking corn and soy while also drawing support from brisk global demand and Ukraine considering limits on exports, analysts said. Technical buying helped boost the markets in pre-holiday trading, traders said. The most-active soybean contract closed up 22-1/4 cents at $13.35 a bushel, extending gains for a seventh day and reaching the highest price since Aug. 25. Most-active CBOT corn rose for a second session, ending up 4-1/4 cents at $6.02-1/2 a bushel and topping the $6 level for the first time since July 1. "South American weather is concerning for the southern part of Brazil and Argentina as dry weather looks to persist to the end of the year," CHS Hedging said. Drought in southern Brazil and developing dryness in parts of Argentina have tempered earlier optimism about South American harvest prospects. Crop losses in South America could shift export demand to the United States. "The 15-day weather forecast does not point to any improvement," consultancy Agritel said. Most-active CBOT wheat settled up 15 cents at $8.14 per bushel and reached its highest price since Dec. 3. Major global grain producer Ukraine will consider limiting milling wheat exports in the first half of 2022, two sources familiar with the discussions told Reuters. Russia, the world"s top wheat exporter, has sought to curb shipments since early this year, leaving major importers scrambling to find alternative supply. read more On Thursday, the U.S. Department of Agriculture will issue weekly export sales data for grains and soybeans. Tuesday"s purchase of 320,000 tonnes of milling wheat by Turkey"s state grain board and news that Iran"s Government Trading Corporation issued another wheat import tender underscored strong international demand, traders said. Reporting by Tom Polansek in Chicago, Gus Trompiz in Paris and Emily Chow in Beijing; Editing by Vinay Dwivedi, David Evans, Ramakrishnan M and Sonya Hepinstall