Newly-imposed US sanctions against two Russian energy ministry officials are “unlawful” and Moscow will seek explanations from Washington, Russian Energy Minister Alexander Novak says.

The US added Russian officials and energy firms to a sanctions blacklist on Friday, days before details of further possible penalties against Moscow are due to be released.

“We consider it to be absolutely unlawful, they haven’t presented us with any arguments. We will expect some explanations on this,” Novak was quoted as saying by TASS news agency.

One person added to the list was Russian Deputy Energy Minister Andrey Cherezov, who was put under sanctions by the European Union over his role in the delivery of turbines to Crimea last year.

Russia is already under US sanctions over its annexation of Crimea from Ukraine in 2014 and support for separatist rebels fighting in eastern Ukraine.

On Friday, the US Treasury said it had added 21 people and nine companies to the sanctions list, including some that involved in the delivery of Siemens gas turbines to Crimea.

Novak dismissed the impact of the sanctions.

“The sanctions only create additional conditions for domestic industry development,” he said, according to TASS.

Novak also said he met US Energy Secretary Rick Perry during an economic forum in Davos this week and invited him to visit the Russian Yamal LNG plant, which started producing liquefied natural gas in December.

Russia has been watching growing oil production in the US with concern, as Moscow has curbed oil output jointly with the Organisation of the Petroleum Exporting Countries in order to reduce excessive inventories and prop up oil prices.