Wheat prices have risen sharply on global markets after Russia said it would treat ships heading for Ukrainian ports as potential military targets.
Moscow has pulled out of a UN deal on that ensured safe passage for grain shipments crossing the Black Sea.
Since then Russia has been bombarding Ukraine’s grain facilities in Odesa and other cities.
Moscow also warned that ships going there would be seen as siding with "the Kyiv regime".
Meanwhile, Ukraine has said ships heading towards Russian or occupied ports on the Black Sea could be viewed as carrying military cargo.
Clive Myrie presents BBC News at Ten reporting by Paul Adams and Steve Rosenberg.
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