Three people were wounded and a search was underway for seven workers from the Chernomorneftegaz energy company, Sergei Askyonov, the Russian-installed head of Crimea, said in a post on Telegram.

Crimean officials said work on three drilling platforms had been suspended after the hit, with fires reported.

Reuters was unable to immediately verify the reports.

Ukraine’s military declined to comment.

Russian-backed officials seized Chernomorneftegaz from Ukraine’s national gas operator Naftogaz as part of Moscow’s annexation of the peninsula in 2014.

The company is under US and European Union sanctions.

Askyonov said Ukraine hit the platform at 8am local time, when 109 people were working on platforms in the area.

The rigs are located off Ukraine’s south coast in the Black Sea, 71km from Odessa, the RIA Novosti news agency reported, citing Olga Kovitidi, a senator representing Crimea in Russia’s upper house of parliament.

Russian officials have expressed concern over Ukrainian military figures saying they would like to target Crimean infrastructure – such as the Kerch bridge linking Crimea to Russia – as part of a Ukrainian counter-offensive in the south.