Russia has an approaching deadline that will add urgency to its campaign in Ukraine over the coming three weeks, the British defense ministry said.

In its daily intelligence update on the Russian invasion, U.K. defense officials said that Moscow wants big military gains before its annual commemoration of the end of World War II on May 9.

The commemoration of the USSR's role in defeating Nazi Germany is celebrated across Russia, where World War II is known as the Great Patriotic War.

The defense ministry said Moscow "likely desires to demonstrate significant successes ahead of their annual 9th May Victory Day celebrations."

"This could affect how quickly and forcefully they attempt to conduct operations in the run-up to this date."

Russian forces are now advancing in the eastern Donbas region as part of a renewed offensive after failing to take Kyiv.

The assessment by British defense officials said that there have been high levels of Russian air activity to support its offensive in eastern Ukraine and that Russian forces aimed "to suppress and destroy Ukrainian air defense capabilities."