The following is the March 16, 2022, Congressional Research Service Legal Sidebar, The Law of War and the Russian Invasion of Ukraine.
From the report
In the days after Russia’s invasion of Ukraine on February 24, 2022, many countries condemned the action as a violation of international law governing when countries may use force against one another. Since then, several observers, including the U.S. Secretary of State and other foreign government officials, have cited evidence that the Russian...
https://news.usni.org/2022/03/25/report-to-congress-on-law-of-war-and-the-invasion-of-ukraine