Russia has banned oil sales to countries and companies that comply with a price cap agreed by Western nations earlier this month.
The price cap - which was agreed by the G7 group of nations, Australia and the EU - came into force on 5 December.
The cap prohibits countries from paying more than $60 (€56; £50) per barrel of Russian oil.
Russia has now said its oil and oil products will not be sold to anyone imposing the price cap.
The presidential decree said the ban would take effect for five months from 1 February until 1 July.
The decree also said Russian President Vladimir Putin could give "special permission" to supply to countries that fall under the ban.
The G7 group of major economies first put forward the idea of a price cap in September in order to stop Moscow from using oil revenue to finance the war in Ukraine.