Former Russian President Dmitry Medvedev has warned U.S. President Donald Trump about the danger of World War III after Trump criticized Russian President Vladimir Putin.

Trump recently said he would definitely consider adding new sanctions on Russia. This comes as Ukraine continues to suffer from missile and drone attacks, causing many deaths.

Medvedev posted on social media that Trump’s words about Putin “playing with fire” could lead to something very serious — World War III. He hopes Trump understands how dangerous this is.

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

Trump’s anger has grown after a recent Russian drone strike killed at least 13 people in Ukraine. He is frustrated that he has not been able to stop the war, even though he once said he could end it quickly.

While talks to end the war have increased recently, Putin has been accused of delaying peace negotiations.

On Tuesday, Trump warned that there would be “serious consequences.” He told Putin that if it weren’t for him, worse things would have already happened to Russia. He said Putin was “playing with fire.”

Although Trump did not explain exactly what the consequences might be, news reports say the U.S. could announce new sanctions on Russia soon. Trump also said on Sunday that he is seriously thinking about this step.

Russia, which invaded Ukraine in February 2022, has not yet responded directly to Trump’s recent comments. Earlier, Russian officials blamed Ukraine for making the conflict worse and said they are defending their civilians.

In recent days, Russian authorities say they have stopped almost 150 drones sent from Ukraine, including 33 heading toward Moscow.

The situation between Russia, Ukraine, and the U.S. remains tense, with the threat of further conflict looming as leaders exchange warnings and consider new actions.