President Biden on Tuesday for the first time accused Russia’s President, Vladimir V. Putin, of perpetrating genocide on the Ukrainian people, but emphasised that was his personal view, not a legal determination.

The remark initially came off-handedly in a speech at a bio-ethanol plant in Iowa, in which Biden was announcing measures to counteract rising gas prices. About halfway through the speech, he made reference to Putin and the war’s economic impact on Americans.

“Your family budget, your ability to fill up your tank, none of it should hinge on whether a dictator declares war and commits genocide half a world away,” Biden said. It was a marked escalation from statements earlier this month, when he said Russian atrocities in the suburbs near the Ukrainian capital, Kyiv, amounted to war crimes, but did not rise to the level of genocide.

On the tarmac later on Tuesday afternoon as he left Iowa, the president reaffirmed his characterisation.

“Yes, I called it genocide. It has become clearer and clearer that Putin is just trying to wipe out the idea of even

being able to be Ukrainian,” he said.

“We’ll let the lawyers decide internationally whether or not it qualifies,” he added, “but it sure seems that way to me”.

President Volodymyr Zelensky of Ukraine, who has repeatedly accused Russia of genocide, welcomed Biden’s comments. “True words of a true leader,” he wrote on Twitter.

“Calling things by their names is essential to stand up to evil.”

Biden’s comment is not the same as a formal determination of genocide by the US government, which has happened only eight times and triggers legal obligations under the Genocide Convention, which the US ratified in 1988. States are required to prevent and punish genocide, and grant extradition when genocide charges are involved.

In international law, genocide is defined as killing or causing serious bodily or mental harm “with intent to destroy, in whole or in part, a national, ethnical, racial or religious group”.

Zelensky, speaking from Kyiv, asked what kind of plan could account for the heavy casualties suffered by Russian forces since the war began in February. American officials said last month that a conservative estimate put the Russian death toll at more than 7,000.

“Who could approve such a plan?” Zelensky said.