The Kremlin is yet to officially comment on the new deadline. But Dmitry Medvedev -- the former Russian president and prime minister now serving as the deputy chairman of the country's Security Council -- framed Trump's challenge as a dangerous escalation.

Trump in July set a 50-day deadline for the agreement with Ukraine, threatening tariffs if a deal was not made. On Monday, during his meeting with U.K. Prime Minister Keir Starmer, he said he was shortening this deadline to “10 or 12 days.”