U.S. President Donald Trump and Russian Security Council Deputy Chairman Dmitry Medvedev exchanged barbs on social media Thursday, as tensions flared over stalled U.S.-India trade talks and the looming threat of new tariffs.

The spat came as negotiations between Washington and New Delhi appeared to hit an impasse just days ahead of a deadline set by Trump. Frustrated by what he called “unacceptable trade barriers,”  the U.S. president also slammed India’s ongoing purchases of Russian oil and weapons, threatening to impose a 25% tariff on Indian exports.

“I don’t care what India does with Russia,” Trump wrote on his Truth Social platform. “They can take their dead economies down together, for all I care.”

Turning his fire on Moscow, Trump added: “Russia and the USA do almost no business together. Let’s keep it that way, and tell Medvedev, the failed former President of Russia, who thinks he’s still President, to watch his words. He’s entering very dangerous territory.”

It was not immediately clear what comments by Medvedev prompted the outburst. The last English-language post by the former Russian president on X was made more than a month ago, when he responded to earlier criticism from Trump over U.S. strikes on Iran and Tehran’s nuclear program.

Trump’s comments also follow his recent ultimatum to the Kremlin, warning that Moscow has until Aug. 8 to reach a peace deal with Ukraine or face new sanctions.

Later Thursday, Medvedev fired back in a post on Telegram.

“If a few words from the former president of Russia can provoke such a jittery reaction from the mighty president of the United States, then Russia must be completely in the right,” he wrote. “We’ll keep moving forward on our own path.”

Medvedev then mocked Trump’s “dead economies” remark, referencing Cold War nuclear strategy.

“As for ‘dead economies’ and ‘dangerous territory,’ maybe he should rewatch his favorite zombie movies and remember just how dangerous the so-called ‘Dead Hand,’ which doesn’t even exist, can be,” Medvedev wrote, ending the message with a laughing emoji.

The “Dead Hand” is a Cold War-era term describing a hypothetical Soviet doomsday device that could launch a nuclear counterstrike even if the country’s leadership was wiped out.

Medvedev, who served as Russia’s president from 2008 to 2012, has adopted increasingly hawkish rhetoric since the Kremlin launched its full-scale invasion of Ukraine in 2022. He has repeatedly invoked nuclear threats in messages aimed at the West.

In May, Trump’s special envoy for Ukraine, Keith Kellogg, accused Medvedev of stoking fears of World War III after the Russian official responded to Trump’s warnings that Putin was “playing with fire.”