US futures tumbled to a near one-month low on Wednesday amid a broad sell-off on grains markets and still under pressure after Russia, the world's top wheat supplier, raised its grain export forecast last week.

Benchmark March milling wheat on Paris-based Euronext settled at 203.25 euros a tonne, down 0.85 percent.

Most active wheat on the Chicago Board of Trade was down 0.5 percent after falling 1.3 percent on Wednesday.

"Euronext was closed during more than two sessions but grains tumbled in Chicago yesterday. This is just a catch-up effect," a trader said.

Morocco said it would suspend its customs duty on soft wheat for four more months until April 30 next year to maintain price stability and ensure regular supply.

It had said in October that it would impose a 30 percent customs duty starting on Jan. 1.

The decision will favour wheat exports to Morocco but is not necessarily good news for French wheat, which benefits from a preferential tariff agreement. The cancellation of the customs duty on soft wheat puts all competitors on the same level.