Ukraine welcomes the extension of the Black Sea grain export deal but Russia must not be allowed to sabotage the agreement and must stop using food "as a weapon and blackmail," Reuters reported, citing a senior Ukrainian official on Wednesday.

"We welcome the continuation of the initiative, but emphasise that it must work effectively," Deputy Prime Minister Oleksandr Kubrakov said on Facebook.

"We hope that our partners will make every effort to ensure that the grain deal starts to work fully for the world's food security, and that Russia will finally stop using food as a weapon and blackmail," he added.

The United Nations and Turkey brokered the Black Sea deal for an initial 120 days in July last year to help tackle a global food crisis that has been aggravated by Moscow's invasion of Ukraine, one of the world's leading grain exporters.

Turkish President Tayyip Erdogan said on Wednesday the deal had been extended for two more months.

Ukrainian officials have said that since mid-April, Russia has "unreasonably restricted" the work of the deal. Russia has denied this.

Almost 70 vessels are currently waiting in Turkish waters for inspections.