Sen. Bernie Sanders was informed by U.S. intelligence officials that Russia is trying to help his presidential campaign, the Washington Post reported on Friday.

Members of Congress and President Donald Trump have also been briefed by U.S. officials, the Washington Post added.

Sanders addressed the Washington Post's report while campaigning in California on Friday. Sanders warned Putin to "stay out of American elections."

“Unlike Donald Trump, I do not consider Vladimir Putin a good friend," Sanders said. "He is an autocratic thug who is attempting to destroy democracy and crush dissent in Russia. Let’s be clear, the Russians want to undermine American democracy by dividing us up and, unlike the current president, I stand firmly against their efforts, and any other foreign power that wants to interfere in our election."

It is unclear to how exactly the Kremlin is trying to boost Sanders' campaign.

US officials have been investigating Russian involvement in domestic presidential elections since the 2016 election.

Special Counsel Robert Mueller brought charges against 13 Russian officials for conspiring to defraud the United States. Mueller alleged that Russian oligarchs conspired to help Trump get elected.