Hackers broadcast a fake emergency televised appeal from a computer-generated Russian President Vladimir Putin declaring martial law after Ukrainian troops crossed into Russian territory, the Kremlin told state media on Monday.

A number of radio and television stations in border regions aired the message, purportedly from the country’s commander in chief. On screen, a realistic-looking Putin declared that a full-scale mobilization would begin in preparation for all-out war with Ukraine, while urging citizens to evacuate their homes and seek safety further inside Russia.

“Today, at 4 am this morning, Ukrainian forces … with the support of Washington, entered the territory of Kursk, Belgorod and Bryansk regions,” the broadcast said, announcing a mass call-up of eligible men to “defeat the dangerous and perfidious enemy.”

However, in a statement issued Monday, Putin’s press secretary, Dmitry Peskov, insisted that the speech “definitely didn’t happen.” Instead, he said, security services were looking into the matter. Television operators in Crimea, occupied by Russia since 2014, confirmed their systems had been compromised.

“Fake posts purporting to come from real figures are an increasing risk in an AI-influenced world,” said Colonel Philip Ingram, a former British military intelligence officer and NATO planner. “In war propaganda, ‘deepfakes’ delivered in a convincing way for military or political effect, they’re an expected weapon — but they can be very convincing.”

The apparent cyberattack comes after a spate of cross-border raids by pro-Ukrainian fighters under the banner of the Legion of Free Russia and the Russian Volunteer Corps, said to be Russian citizens intent on fighting against Putin’s rule. On Sunday, one of the groups said it had taken dozens of prisoners during one such incursion and would exchange them for captured Ukrainian soldiers.

Efforts to put Moscow’s forces on the back foot and force them to commit scarce manpower and weaponry defending the 1,000-kilometer shared border have escalated amid growing expectations that Kyiv will launch a major assault to retake territory occupied by Russia.

Ukraine’s Deputy Defence Minister Hanna Maliar said on Monday that the country’s troops are  “shifting to offensive actions” along some parts of the front line. Meanwhile, the commander of Kyiv’s ground forces, General Oleksandr Syrskyi, said his units were “moving forward” towards the contested city of Bakhmut.

“The Ukrainian side — or those acting on their behalf — is playing a clever game by using Russia’s long-trialed tactics for disseminating chaos against them,” said Ian Garner, an expert on Russian propaganda and author of a new book on the war. “With a constant barrage of videos and news of stories that blur the line between truth and reality, pro-Ukrainian actors can keep the Russian population on their toes.”