CHICAGO, Feb 1 (Reuters) - U.S. soybean futures fell about 1.5% on Thursday on disappointing weekly U.S. export sales data coupled with strong competition from Brazil, where the soy harvest is expanding, traders said.

Corn sagged in sympathy with soybean futures while wheat futures turned higher on technical buying.

Chicago Board of Trade (CBOT) March soybeans settled down 19 cents at $12.03-1/4 per bushel. CBOT March corn ended down 1 cent at $4.47-1/4 a bushel while March wheat finished up 6-1/4 cents at $6.01-1/2 a bushel.

Soybeans slumped after the U.S. Department of Agriculture (USDA) reported old-crop U.S. soybean export sales in the week to Jan. 25 at 164,500 metric tons, the lowest weekly tally for the 2023/24 marketing year that began Sept. 1.

Traders largely shrugged off news that the USDA separately confirmed private sales of 206,834 tons of U.S. soybeans to Mexico.

Demand for U.S. soy has been hampered by strong competition from Brazil, where cash soybean prices have been falling, as well as economic woes in China, by far the world's largest soybean buyer.

"Part of it is the Chinese economy; demand is not picking up on the breaks (in price) the way you would think. It feels like the buyers are waiting to get further into Brazil's harvest," said Don Roose, president of U.S. Commodities.

Uncertainty about the exact size of Brazil's soybean crop underpinned the market. StoneX, a brokerage, lowered its Brazilian soy production estimate to 150.35 million metric tons, from 152.8 million a month ago.

Corn futures followed soybeans lower, but declines were limited by brisk weekly U.S. corn export sales of more than 1.2 million tons, near the high end of trade expectations.

StoneX estimated Brazil's total corn harvest at 124.5 million tons, practically unchanged from last month.

CBOT wheat futures rose on bargain buying, with the spot March contract clawing back above psychological support at $6 a bushel.

Euronext wheat futures turned higher after hitting contract lows, but ongoing worries about weak demand and competition from Black Sea supplies continued to anchor prices.

Low prices in Europe have led to widespread protests. (Reporting by Julie Ingwersen; additional reporting by Peter Hobson in Canberra and Nigel Hunt in London; Editing by Paul Simao and David Gregorio)