US President Biden says Russia's Putin is 'war criminal'

US President Joe Biden on Wednesday said he believes Russian President Vladimir Putin is a "war criminal" as Moscow's war on Ukraine is about to enter its fourth week.

"I think he is a war criminal," Biden told a reporter in an exchange.

His remarks came a day after the US Senate passed a resolution seeking to back an investigation of war crimes into the Russian president for the war in Ukraine.

Reports have repeatedly come out from Ukraine of Russian forces targeting civilian premises, including maternity hospital and a theatre in Mariupol city where people were seeking shelter from shelling.

"We consider unacceptable and unforgivable such rhetoric of the head of state, whose bombs killed hundreds of thousands of people around the world," TASS news agency quoted Kremlin spokesman Dmitry Peskov as saying.

Biden also authorized on Wednesday $800 million in new assistance for Ukraine to bolster its forces in the face of the ongoing war. The new aid package includes Stinger anti-aircraft systems, Javelin anti-tank missiles, light anti-armor weapons, anti-armor systems, tactical unmanned aerial systems as well as rifles and ammunition.

Russia's invasion of Ukraine, which began Feb. 24, has drawn international condemnation, led to financial sanctions on Moscow, and spurred an exodus of global firms from Russia.

At least 726 civilians have been killed and 1,174 injured in Ukraine since the beginning of the war.

More than 3 million refugees have fled to neighboring countries, according to the UN.