Ukrainian President Volodymyr Zelensky on Sunday thanked Berlin for its backing in Kyiv's battle against Moscow troops, calling Germany a "true friend" during his first visit since Russia's invasion.

"In the most challenging time in the modern history of Ukraine, Germany proved to be our true friend and reliable ally, which stands decisively side-by-side with the Ukrainian people in the struggle to defend freedom and democratic values," he wrote in the guestbook at the German president's official residence.