Poland has imposed sanctions on Gazprom Export, a unit of Russia's gas company that exports natural gas, the interior ministry said on Thursday.

In April, Poland imposed sanctions on 50 Russian oligarchs and companies, including Gazprom, in a move to increase pressure on Moscow over its invasion of Ukraine. Simultaneously, Russia halted gas exports to Poland as Warsaw refused to pay in roubles.

Under the latest decision Gazprom Export's assets will be frozen. Access to financial funds and economic assets of the sanctioned company is banned, the ministry said.

It added that the company's deputy head Mikhail Sereda had been put on the sanctions list by the United States.

"The activities of Gazprom Export LCC are of strategic importance for the government of the Russian Federation," the ministry said on its website.