Russia's Prime Minister Dmitry Medvedev reportedly warned the U.S. on Friday that sanctions it plans to impose against Moscow over the nerve-agent attack of a former spy living in Britain could be treated as a declaration of an economic war.

Speaking during a trip to the Kamchatka region of Russia, Reuters reported Medvedev as saying: "I would not like to comment on talks about future sanctions, but I can say one thing: If some ban on banks' operations or on their use of one or another currency follows, it would be possible to clearly call it a declaration of economic war."

"And it would be necessary, it would be needed to react to this war economically, politically, or, if needed, by other means. And our American friends need to understand this," he added.

President Donald Trump's administration said Wednesday it plans to punish Russia with sanctions for poisoning Sergei Skripal and his daughter Yulia Skripal with a chemical weapon earlier this year. In a statement, spokeswoman Heather Nauert said the sanctions will go into effect around August 22.

Skripal, a former Russian spy who became a double agent for the U.K., fell into critical condition after being poisoned in Britain on March 4. His daughter Yulia, who was visiting him from Moscow, was also poisoned.