Chicago wheat futures regained ground on Wednesday as the outcome of diplomatic discussions to allow sea exports of Ukrainian grain remained uncertain in the run-up to summer harvesting.
Corn extended gains to a one-week high while soybeans continued a rally to hit a three-month top, as doubts over availability of Ukrainian supplies added to support from a firm US cash market and drier weather forecast for the Midwest.
The most-active wheat contract on the Chicago Board of Trade (CBOT) was up 0.8% at $10.80-1/4 a bushel by 1215 GMT.
The benchmark has fluctuated this week, jumping 5% on Monday before falling back nearly 2% on Tuesday, as participants assessed news about potential exports from war-torn Ukraine.
Comments by Russian and Turkish officials on Tuesday raised hopes about progress towards a Black Sea shipping channel for Ukrainian grain cargoes.
However, Ukraine's foreign ministry on Wednesday said Russian assurances it would not take advantage of a port reopening for its military campaign were "empty words".
While the Kremlin put the onus on Ukraine to agree to grain shipments Russia also said sanctions should be lifted to allow Russian grain to reach the international market.
"Volatility remains high in a market still driven by the Russian-Ukrainian conflict," consultancy Agritel said.
"There are obviously many doubts about the positive conclusion of the ongoing talks with Russia and Turkey."
CBOT corn was up 1.4% at $7.67-1/2 a bushel after climbing to its highest since 31 May.
Soybeans also added 1.4%, to $17.51-3/4 a bushel, after earlier reaching their highest since late February.
Spot basis bids for corn strengthened at rail terminals, processors and elevators across the US Midwest on Tuesday, grain dealers said.
Attention is turning towards monthly US Department of Agriculture crop forecasts.
Analysts on average expect the USDA to trim its projections for US corn and soybeans stocks.