Four people were killed and fuel sales were suspended in annexed Crimea, the Moscow-backed authorities there said on Sunday, after a massive Ukrainian barrage hit the Black Sea peninsula.

Ukraine said it targeted military and energy facilities in Crimea — Moscow's key logistics base for its four-year military offensive — in one of the biggest attacks on the peninsula in recent months.

"As a result of the enemy's drone attack on the Kerch Peninsula, unfortunately, there are casualties among the civilian population," said Russia-backed Crimea Governor Sergey Aksyonov, referring to the part of Crimea that borders Russia.

"According to the latest information, four people were killed, 28 were wounded," he added.

"Today, June 21, starting from 09:00 am, fuel sales at Crimean petrol stations have been suspended," said Aksyonov in a separate statement, adding that fuel would only be sold to state enterprises.