Russian Energy Minister Sergei Tsivilev said on Wednesday that Russia was supplying fuel to Cuba as humanitarian aid.
Tsivilev, who was speaking to reporters on the sidelines of the ministry's conference, did not elaborate further.
The US Treasury Department on Thursday changed the terms of a waiver it had granted to sales of Russian-origin crude and petroleum products already loaded on tankers to specifically exclude transactions involving North Korea, Cuba and Crimea.
Power blackouts are now the norm in Cuba, which has received only two tankers at its ports this year bringing imported oil cargoes, LSEG data showed.
A tanker carrying fuel originally bound for Cuba on Friday changed its destination to Trinidad and Tobago, according to LSEG ship-tracking data, a blow for the island amid a severe fuel scarcity that has triggered power blackouts.
(Reporting by Olesya Astakhova; writing by Vladimir Soldatkin Editing by Tomasz Janowski)