The props were simple, the message was clear. In a video address to the nation this week, Ukrainian President Volodymyr Zelenskyy held up his smartphone to the camera and started a timer app while an air raid siren blared.

"It lasted 20 seconds," Zelenskyy said, after the wailing subsided. "And we hear it for hours, days, weeks. Our people ... instantly take their children, help the elderly, and go to the shelters ... to survive, from Russian missiles, bombs."

Sitting at his desk, unshaven and in his now trademark green shirt, Zelenskyy had in a few short sentences reminded 44 million Ukrainians that he was going through what they were, while renewing pressure on NATO to impose a no-fly zone.