* Hot U.S. weather expected to ease in coming days
* Traders expect USDA to trim corn, soy ratings Monday
* Ukraine says Russia threatened civilian vessels
CHICAGO, July 28 (Reuters) - Chicago Board of Trade grain and soybean futures fell to their lowest prices in more than a week on Friday on hopes that U.S. crop weather will improve and Russia will ease its attacks on Ukraine's grain facilities, analysts said.
Technical selling added pressure to prices.
Heading into August, the key period of development for U.S. soybean crops, much of the country is expected to get a reprieve from significantly above-normal temperatures, the U.S. Department of Agriculture said in a daily weather forecast.
Grain traders said they expect the USDA, in a separate report on Monday, will lower weekly condition ratings for corn and soybean crops because of recent heat.
"All eyes are on the weather daily," said Don Roose, president of broker U.S. Commodities.
The most-active soybean contract slid 15 cents to $13.83 a bushel by 12:05 p.m. CDT (1705 GMT), while front-month soybeans were down 32-1/2 cents at $14.99-1/2. Most-active corn dropped 8-3/4 cents to $5.33-1/2 a bushel, and wheat declined 6-3/4 cents to $7.06 a bushel.
The markets have retreated since touching multi-week highs on Monday.
"After we couldn't extend the early week gains, the trade needed to go and find support," said Matt Wiegand, commodity broker for FuturesOne.
Traders are monitoring fighting in Ukraine after Russia last week quit the Black Sea grain export deal and warned that ships heading to Ukrainian seaports could be considered military targets.
A senior Ukrainian official on Friday accused Russia of threatening civilian vessels in the Black Sea. The Russian military, meanwhile, said it shot down a Ukrainian missile over the southern Russian city of Taganrog.
"The trade is trying to believe there's not going to be any new targets by Russia on grain facilities," Roose said. "We'll see if that's true."
In other news, the USDA said exporters sold U.S. soybeans to China, Mexico and unknown destinations in separate deals. (Reporting by Tom Polansek in Chicago. Additional reporting by Naveen Thukral in Singapore and Sybille de La Hamaide in Paris; Editing by Kirsten Donovan)
