Former Russian President Dmitry Medvedev has issued a stark warning to U.S. President Donald Trump, invoking the threat of World War III following Trump’s criticism of Russian President Vladimir Putin.

The warning came after Trump stated he would "absolutely" consider new sanctions against Moscow, amid continued missile and drone attacks in Ukraine that have left many dead.

In a post on X, Medvedev wrote:

“Regarding Trump’s words about Putin ‘playing with fire’ and ‘really bad things’ happening to Russia — I only know of one REALLY BAD thing: WWIII. I hope Trump understands this!”

Medvedev served as Russia’s president from 2008 to 2012 and as prime minister from 2012 to 2020.

Trump’s frustration over his inability to end the war, which he once claimed he could resolve within 24 hours, intensified over the weekend following a Russian drone strike that killed at least 13 people in Ukraine.

Diplomatic efforts to end the war have ramped up in recent weeks, but Putin has been accused of stalling peace negotiations.

Speaking on Tuesday, Trump warned of “serious consequences,” saying: “What Vladimir Putin doesn’t realise is that if it weren’t for me, lots of really bad things would have already happened to Russia — and I mean REALLY BAD. He’s playing with fire!”

While Trump did not elaborate on the nature of the consequences, The Wall Street Journal and CNN reported that new U.S. sanctions on Russia could be announced as early as this week. On Sunday, Trump told reporters he was “absolutely” considering the move.

Russia, which invaded Ukraine in February 2022, has yet to respond directly to Trump’s latest comments. However, earlier statements from Moscow blamed Ukraine for escalating tensions and claimed it was responding to increased attacks on Russian civilians.

Russian authorities reported intercepting nearly 150 Ukrainian drones in recent days, including 33 that were heading toward Moscow.