U.S. wheat and soybean futures edged lower on Thursday as a six-session rally stalled in the face of ample global supplies of the crops and as investor awaited the outcome of a closely watched European Central Bank policy meeting.

The most active Chicago Board of Trade soybeans future was down 0.1 percent at $8.84-1/2 a bushel, as it eased back from Wednesday's five-week high of $8.88 a bushel.

The most active CBOT wheat contract also edged down 0.1 percent, to $4.67-3/4 a bushel, just off a three-week peak of $4.68-1/2 touched in each of the two previous session.

Corn fell 0.4 percent to $3.58-1/4 a bushel, after also falling slightly on Wednesday.

Wheat and soybeans drew some support from downward revisions to world stocks in the U.S. Department of Agriculture's (USDA) monthly supply and demand data on Wednesday.

This added to recent support from adverse weather for U.S. wheat belts and brisk export demand for soybeans, but traders said the USDA's report broadly confirmed a large global surplus.

"The monthly USDA report hasn't changed the situation. Even though some small corrections have been made on final stocks, fundamentals remain heavy," consultancy Agritel said in a note. "Today, markets will pay attention to the ECB's meeting with possible consequences on the euro-dollar."

The USDA trimmed global soy stocks to 78.87 million tonnes, below forecasts ranging from 80 million to 82 million tonnes. It also cut world wheat stocks by more than expected but the stockpile remained the largest on record.

In a bearish move for the U.S. soy market, the agency raised its outlook for U.S. soybean ending stocks in 2015/16 to above market expectations.

Financial markets were focused on Thursday's ECB policy meeting that is expected to see the central bank lower its deposit rate further into negative territory and to expand its bond-buying program.

Grain traders were also awaiting weekly U.S. export sales data at 1330 GMT for a fresh indication of demand.