KYIV (REUTERS) - President Volodymyr Zelensky posted a video on Instagram from his office on Thursday (July 21) to reassure Ukrainians that he is well after what he said was a fake news report about his health by Russian hackers.

Zelensky, 44, made his remarks on the same day that the Kremlin dismissed what it said were false reports that Russian President Vladimir Putin was unwell.

His Instagram post appeared after a Ukrainian media company said hackers had broadcast a false report about Zelensky's health on one of its radio stations following a cyberattack.

"Today, Russia launched more fake news that the (Ukrainian) state is not controlled by President Zelensky as he is in hospital, or rather, in intensive care because of a 'serious health condition'," Zelensky said.

"So, here I am in my office, and I have never felt as good as now," he said, sitting as a desk and wearing a khaki T-shirt.

"And the bad news for those behind such fakes is that I am not alone. There are 40 million of us (Ukrainians)."

In an apparent dig at Putin's age, he said: "And with all due respect to old age, 44 is not (almost) 70."

Russia, which invaded Ukraine on Feb 24, did not immediately comment on Zelensky's remarks.