Washington, Mar 17 (IANS): For the first time since Moscow waged its war on Kiev on February 24, US President Joe Biden called his Russian counterpart Vladimir Putin a "war criminal" as the latter is "inflicting appalling devastation and horror on Ukraine".

Biden made the remarks while responding to a reporter's question at the White House on Wednesday, the BBC reported.

When the reporter asked the President is he was ready to call Putin a "war criminal", Biden responded by saying: "Did you ask me whether I would tell ....? Oh, I think he is a war criminal."

Later in a tweet, the American leader said: "Putin is inflicting appalling devastation and horror on Ukraine - bombing apartment buildings and maternity wards.

"Yesterday (Tuesday), we saw reports that Russian forces were holding hundreds of doctors and patients hostage. These are atrocities. It is an outrage to the world."

Also in a statement, White House Press Secretary Jen Psaki said that Biden's branding of Putin as a "war criminal" came as the US President had been "speaking from his heart" after seeing "barbaric" images of the violence in Ukraine, "rather than making any official declaration", reports the BBC.

She noted that there was a separate legal process, run by the State Department, to determine war crimes, which was was ongoing separately.

But Biden's remark did not go down well with Russia, which may further escalate diplomatic tensions amid the ongoing war.

"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," the BBC quoted Kremlin spokesman Dmitry Peskov as saying to Russia's state-run TASS News Agency.