Biden's outburst came after Russia targeted civilian apartments, care homes and even hospitals during it's three week war with Ukraine.
President Vladimir Putin of Russia has been called a war criminal by President Joe Biden of the United States .
This comes after Russia invaded Ukraine and started a bloody war that has claimed many lives.
Biden called Putin a war criminal while delivering an off the script remark on Wednesday, March 16 in response to a reporter's question at the White House, making it the first time he has used such language to condemn President Putin.
Russia has targeted civilian apartments, care homes and even hospitals during it's three week war with Ukraine, inflicting deaths on the young, elderly and even new borns, leading many to allege he's commited war crimes, but US officials have been wary of calling him a 'war criminal' yet.
The exchange in Washington happened Wednesday when a reporter asked the US president: "Mr President, after everything we have seen, are you ready to call Putin a war criminal?"
Biden replied "no" before being challenged, and then changed his reply: "Did you ask me whether I would tell ....? Oh, I think he is a war criminal."
White House Press Secretary Jen Psaki later said the president had been speaking from his heart after seeing "barbaric" images of the violence in Ukraine, rather than making any official declaration.
She noted that there was a separate legal process, run by the State Department, to determine war crimes - and that was ongoing separately.
The president's official Twitter account posted: "Putin is inflicting appalling devastation and horror on Ukraine - bombing apartment buildings and maternity wards... these are atrocities. It is an outrage to the world."
Responding to Biden's statement, thr Kremlin, said it was "unforgiveable rhetoric".
"We believe such rhetoric to be unacceptable and unforgivable on the part of the head of a state, whose bombs have killed hundreds of thousands of people around the world," spokesman Dmitry Peskov told Russian state news agency Tass.
Also on Wednesday, Putin gave a televised speech laced with rhetoric against the West.
He accused the West of trying to divide Russia with lies, and railed against those he called "traitors" inside of Russia.
"Of course they will try to bet on the so-called fifth column, on traitors - on those who earn their money here, but live over there. Live, not in the geographical sense, but in the sense of their thoughts, their slavish thinking," Putin said.
The term "fifth column" is used for a group that try to undermine a nation or organisation from the inside.
"Any people, and especially the Russian people, will always be able to distinguish the true patriots from the scum and the traitors, and just to spit them out like a fly that accidentally flew into their mouths," he said.
Putin then accused the West of trying to provoke civil conflict with the goal of "the destruction of Russia".