Officials have said Russian strikes hit the Ukrainian port of Odesa, Thursday for a third consecutive night since Moscow pulled out of a grain export deal, as Crimean authorities said a teenager had died in Kyiv's latest attack on the peninsula.

At least 20 people were wounded following strikes on Odesa and the southern port city of Mykolaiv, local officials said, posting images showing buildings in flames with facades partially destroyed.

An "administrative building" in Odesa's city centre was destroyed and others damaged, according to a spokeswoman for Ukraine's southern military command, who said details were still being clarified.

A previous round of overnight strikes on Odesa destroyed 60,000 tonnes of grain meant for export, Kyiv said on Wednesday, with President Volodymyr Zelensky accusing Moscow of "deliberately" targeting the supplies.

Moscow's invasion of Ukraine last year saw Black Sea ports blocked by warships until the gain agreement, brokered by the United Nations and Turkey in July 2022.

The Kremlin said on Monday it was exiting the deal, after months of complaining that the pact that had allowed the export of Russian food and fertilisers had not been honoured.

The deal enabled the export of more than 32 million tonnes of Ukrainian grain over the last year, bringing relief to countries facing critical food shortages such as Afghanistan, Sudan and Yemen.

Wheat prices soared on the European stock exchange on Wednesday.

Also Wednesday Moscow said it would consider cargo ships travelling to Ukraine through the Black Sea as potential military targets.

A senior United States security official later told AFP that Russia was considering attacking civilian ships on the Black Sea and putting the blame on Kyiv.

National Security Council spokesman Adam Hodge cited Russia's release of a video showing its forces detecting and destroying an "alleged Ukrainian sea mine".

"Our information indicates that Russia laid additional sea mines in the approaches to Ukrainian ports," he said.

"We believe that this is a coordinated effort to justify any attacks against civilian ships in the Black Sea and lay blame on Ukraine for these attacks."