Sen. John McCain (R-AZ) on Tuesday warned that any efforts to improve the United States’ relationship with Russia could backfire, an apparent reference to Russian President Vladimir Putin’s Monday call with Donald Trump, though McCain did not mention the President-elect by name.

“With the U.S. presidential transition underway, Vladimir Putin has said in recent days that he wants to improve relations with the United States,” McCain said in a statement. “We should place as much faith in such statements as any other made by a former KGB agent who has plunged his country into tyranny, murdered his political opponents, invaded his neighbors, threatened America’s allies, and attempted to undermine America’s elections.”

McCain argued that previous attempts by the U.S. to cultivate a better relationship with Russia did not go as planned.

“The Obama Administration’s last attempt at resetting relations with Russia culminated in Putin’s invasion of Ukraine and military intervention in the Middle East. At the very least, the price of another ‘reset’ would be complicity in Putin and Assad’s butchery of the Syrian people,” he said in the statement. “That is an unacceptable price for a great nation. When America has been at its greatest, it is when we have stood on the side those fighting tyranny. That is where we must stand again.”

The Arizona senator did not mention Trump by name, but his statement comes just one day after the President-elect spoke over the phone with Putin.

Following the conversation, Trump’s transition team said in a statement that he “is very much looking forward to having a strong and enduring relationship with Russia.” The Kremlin called for a “return to pragmatic, mutually beneficial cooperation, which would address the interests of both countries as well as stability and safety the world over” and said that Putin and Trump discussed potential to “combine efforts to tackle international terrorism and extremism,” according to Reuters.

Throughout the campaign, Trump praised Putin and said that he would have a “very, very good relationship with Russia.” And Trump indicated in an interview with the Wall Street Journal on Friday that he would shift away from the Obama approach to Syria.

“My attitude was you’re fighting Syria, Syria is fighting ISIS, and you have to get rid of ISIS. Russia is now totally aligned with Syria, and now you have Iran, which is becoming powerful, because of us, is aligned with Syria,” he said. “Now we’re backing rebels against Syria, and we have no idea who these people are.”

Trump added that if the U.S. attacks Assad, “we end up fighting Russia, fighting Syria.”