Moscow is re-grouping troops to take "revenge" on Europe and Ukraine, President Volodymyr Zelensky said Thursday, as Kyiv urges allies to provide longer range weapons to help fight Russia's military operation.

"Now Russia is concentrating its forces. We all know that. It is preparing to try to take revenge, not only against Ukraine, but against free Europe and the free world," Zelensky said at a press conference attended by EU chief Ursula von der Leyen.