CHICAGO, Jan 25 (Reuters) - U.S. wheat and corn futures extended a rally on Tuesday as fears of Russian military action in Ukraine made traders nervous about a potential disruption to supplies from the Black Sea exporters.

Russia has massed an estimated 100,000 troops within reach of Ukraine's border, raising alarm in the West that Moscow is preparing for a new military assault.

Interruptions to grain flows https://www.reuters.com/markets/europe/how-russian-ukraine-conflict-might-hit-global-markets-2022-01-25 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.

Ukraine is projected to be the world's third-largest exporter of corn in the 2021/22 season and fourth-largest exporter of wheat, according to International Grains Council data. Russia is the world's top wheat exporter.

"There is no way of knowing how the conflict between Russia and Ukraine will affect the flow of wheat out of the Black Sea region, but the trade is building risk premium into the wheat market just in case," said Tomm Pfitzenmaier, analyst for Summit Commodity Brokerage in Iowa. "Some of that strength is spilling over into the corn market."

In other news, six major Ukrainian Black Sea ports have restricted grain loading due to poor weather, the state seaport authority said on Tuesday.

The most-active wheat contract on the Chicago Board of Trade (CBOT) soared 29-1/2 cents to $8.30 a bushel by 11:30 a.m. CST (1730 GMT), after earlier reaching its highest since Nov. 29 at $8.31.

CBOT corn was up 6-3/4 cents at $6.27-3/4 a bushel, after earlier reaching its highest since June at $6.31.

Soybean futures also jumped as traders weighed mixed crop prospects in South America and signs of healthy demand for U.S. supplies. CBOT soy rose 7-3/4 cents to $14.10-3/4 a bushel.

Argentine rains in recent weeks brought a "water bomb" to key farming areas in the northwest Buenos Aires province, the Rosario grains exchange said, after drought hit crops.

(Reporting by Tom Polansek in Chicago, Gus Trompiz in Paris and Emily Chow in Beijing; Editing by David Evans and Lisa Shumaker)