The UK has accused Russia of targeting a civilian cargo ship with multiple cruise missiles as it rested in the Ukrainian port of Odesa last month.
The attack – which took place on 24 August – was thwarted by Ukrainian air defences, the UK's foreign office said.
The Liberian-flagged ship was targeted by missiles fired by a Russian carrier, it added.
In July, Russia warned ships travelling to Ukraine's ports through the Black Sea may be seen as military targets.
The warning came after Moscow withdrew from a landmark UN-backed grain deal, which had seen civilian cargo ships promised the freedom to export Ukrainian grain through the Black Sea.
At the time, President Vladimir Putin complained there were too many restrictions on its own agricultural goods.
Moscow also demanded a major Russian bank be let into a global payments system, restrictions be lifted on Russian fertiliser companies, and for its ships to get full access to insurance and foreign ports.
It began a series of strikes on ports in southern Ukraine within days of withdrawing from the deal, which it had pledged not to do under the agreement.
Speaking to parliament on Monday, UK Prime Minister Rishi Sunak said the foiled attack on the grain ship succeeded only in "demonstrating just how desperate Putin is".
"Ukraine has the right to export its goods through international waters and they have the moral right to ship grain that is helping feed the world," Mr Sunak said.
Russia has yet to comment on the attack.
Moscow has increasingly targeted Ukrainian port infrastructure since it pulled out of the grain agreement. Kyiv has accused it of a "cynical" attempt to damage its grain exports and undermine global food security.
In its statement, the Foreign Office said Russia has destroyed 280,000 tonnes of grain since it pulled out of the deal, accusing it of trying to "weaponise food and innocent trade at the expense of the rest of the world".
Officials also said Russian attacks had damaged 26 port infrastructure facilities in Odesa and the nearby ports of Chornomorsk and Reni since July.
In July, Kenyan officials said Russia's withdrawal from the deal amounted to a "stab on the back" for those in drought-hit countries.
Korir Sing'Oei, the top civil servant in Kenya's foreign affairs ministry, said any increase in global food supplies caused by the move "disproportionately impacts countries in the Horn of Africa already impacted by drought".
President Vladimir Putin has pledged to provide free grain to six African nations – all of whom have supported Russia at international forums.
But the foreign office said the amount of grain destroyed by Russian strikes already exceeded the total amount Moscow had pledged to donate to African states, adding that it could have fed up to a million people for a year.
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