PARIS/BEIJING- Chicago and Paris wheat futures extended a rally on Tuesday to one-month highs as fears of Russian military action in Ukraine made investors wary of disruption to supplies from the Black Sea exporters.

A decline in crop ratings in some major U.S. wheat-growing states also lent support to prices. 

Corn was little changed, holding just off a seven-month high as the market monitored tensions over Ukraine, also a major corn supplier.

Soybeans ticked higher to remain near last week's seven-month peak as traders weighed mixed crop prospects in South America and signs of healthy demand for U.S. supplies.

The most-active wheat contract on the Chicago Board of Trade (CBOT) was up 1.3% at $8.10-3/4 a bushel by 1125 GMT, after earlier reaching its highest since Dec. 27 at $8.15-3/4.

March wheat on Euronext added 2.0% to 286.50 euros ($323.14) a tonne.

It also touched its highest since Dec. 27 at 289.25 euros, with additional support from speculation that French wheat may regain access to Algeria's tenders as a diplomatic row between Paris and Algiers subsides.

Investor worries about a possible Russian invasion of Ukraine intensified on Monday as the NATO alliance said it was putting forces on standby and reinforcing eastern Europe with more ships and fighter jets. 

Any interruption to grain flows from the Black Sea region could leave importers scrambling for alternatives, such as European Union and U.S. wheat, and add further fuel to food inflation. 

"Wheat prices ... are the most impacted by the current geopolitical crisis with Russia, with operators pointing to probable supply disruptions," consultancy Agritel said.

Disruption to corn exports from Ukraine could also have a significant impact at a time when drought is expected to trim Brazil's first annual corn crop.

CBOT corn was down 0.04% at $6.20-3/4 a bushel after earlier reaching its highest since last June at $6.21-3/4.

CBOT soybeans inched up 0.07% to $14.04 a bushel.

Rain relief in Argentina and a start to soybean harvesting in Brazil have curbed rallies in corn and soybeans. 

However, analysts have already lowered harvest forecasts and some weather charts showed Argentine weather turning drier again from the end of the month.

($1 = 0.8866 euros)

(Reporting by Gus Trompiz in Paris and Emily Chow in Beijing; Editing by Shailesh Kuber, Subhranshu Sahu and David Evans) ((; +33 1 49 49 52 18; Reuters Messaging: