U.K. Prime Minister Boris Johnson on Saturday said the West must support Ukraine in its effort to recover territory seized by Russia since Russian President Vladimir Putin launched an invasion in February.

Speaking to reporters at England’s air station RAF Brize Norton after returning from an unannounced visit Friday to the Ukrainian capital, Johnson said it would be a “catastrophe” if Putin won the war.

“[It’s] important to go to Ukraine at a particularly critical time,” Johnson said a day after wrapping up his second meeting with Ukrainian President Volodymyr Zelensky in Kyiv since the start of the invasion.

“The worry that we have is