Russian President Vladimir Putin could further escalate his offensive in Ukraine by formally declaring war against the former Soviet state as soon as May 9, according to a report on Monday.

A formal declaration of war against Ukraine would allow the Russian military to mobilize its reserve forces and draft conscripts and then move them to the front lines in the eastern and southern parts of the country, according to the report, which cited U.S. and Western officials. May 9 is a significant date in Russia, known as “Victory Day,” which commemorates the country’s 1945 defeat of the Nazis during World War II. Moscow is slated to host a military parade marking the date.