US President Joe Biden has told Congress that Vladimir Putin badly misjudged how the West would hit back once he invaded Ukraine.
In a primetime speech, Mr Biden vowed “an unwavering resolve that freedom will always triumph over tyranny”.
Democrats and Republicans reacted to Mr Biden’s appeal to show support for Ukraine by rising in unison to applaud.
His State of the Union address came as pandemic-weary Americans grapple with galloping inflation.
In an hour-long address to lawmakers on Tuesday night, the Democratic president said: “Putin’s war was premeditated and unprovoked. He rejected repeated efforts at diplomacy.
“He thought the West and Nato wouldn’t respond. And he thought he could divide us here at home.”
Mr Biden – whose chaotic withdrawal last year from Afghanistan damaged his popularity among Americans – added: “Putin was wrong. We were ready.”
He announced that the US would ban Russian aircraft from American airspace, following similar bans by Canadian and European authorities.
The US and it allies have launched a barrage of sanctions against Russia’s economy and financial system and Mr Putin himself. In his speech Mr Biden deviated from his prepared remarks by vowing further economic retaliation, warning Mr Putin: “He has no idea what’s coming.”
The US president also welcomed Ukrainian Ambassador Oksana Markarova, who received a standing ovation as she sat in US First Lady Jill Biden’s VIP box.
Meanwhile, Russia has stepped up attacks on Ukraine’s biggest cities and Putin has warned residents of Ukraine’s capital Kyiv to flee.