Russia has "deliberately" started a "war" against Ukraine, according to US President Joe Biden.
Russia alone is responsible for the resulting deaths and human suffering, Biden said on Wednesday evening (local time).
The US and its allies are determined to "hold Russia accountable," he said.
Biden said he would continue to monitor the situation at the White House throughout the night and would be briefed by his security team.
In the morning, as already planned, he wants to consult with his counterparts from the group of the seven most important economic nations about how to proceed.
Biden said he would then address the American people to announce further action by the United States and its allies against Russia "for this unnecessary act of aggression against Ukraine and for global peace and security."
"Prayers of the whole world are with the Ukrainians"
"The prayers of the world are with the Ukrainian people tonight as they suffer an unprovoked and unwarranted attack by Russian forces," Biden said.
“President Putin has deliberately chosen a war that will bring catastrophic deaths and human suffering.
Russia alone "is responsible for the death and destruction that this attack will bring," Biden said.
"The world will hold Russia accountable."
NATO Secretary General Jens Stoltenberg has condemned the Russian attack on Ukraine in the strongest possible terms.
The "reckless" attack put "the lives of countless civilians" in danger, Stoltenberg said on Thursday.
Germany has announced serious consequences against Russia because of the announced invasion of Ukraine.
"Russian aggression will have an unprecedented price politically, economically and morally," said German UN Ambassador Antje Leendertse at a short-notice emergency meeting of the UN Security Council in New York on Wednesday evening (local time).
Russia's announcement of war against Ukraine is a military escalation "like we haven't seen in Europe for generations," Leendertse continued.
It is a "shameless breach of international law."
The US, the EU and other allies have already imposed sanctions over Russia's actions in Ukraine.
Biden emphasized on Tuesday that the punitive measures were only initial sanctions that would be significantly expanded if Russia were to invade Ukraine.