U.S. President Joe Biden called Russian President Vladimir Putin a war criminal on Wednesday, prompting the Kremlin to say the comment was "unforgivable" as the war in Ukraine raged for a 21st day despite talk of compromise in peace negotiations.

Moscow has yet to capture any of Ukraine's biggest cities following its incursion that began on Feb. 24, the largest assault on a European state since World War II that has raised fears of wider conflict in the West unthought-of for decades.

Putin on Wednesday said the Kremlin was ready to discuss neutral status for its neighbor but said what he calls a "special military operation" to "demilitarize and denazify" Ukraine was "going to plan."