President Joe Biden will address the nation at 1.30pm ET (6.30pm UK time) on Thursday to outline America’s planned response to Russia’s invasion of Ukraine.

       He is expected to lay out measures that could apply heightened restrictions on Russia’s financial institutions, cut the nation off from advanced technology and impose additional sanctions on Vladimir Putin’s inner circle – actions his administration previously held back in hopes of deterring the long-anticipated invasion.

       The remarks follow two statements issued by the US president in response to Mr Putin’s declaration of a “special military operation” in Ukraine which would aim for the “demilitarisation” of the country.

       Follow live updates on Biden’s response to the Ukraine invasion

       Soon after Mr Putin’s announcement, in a televised speech broadcast just before 6am local time, explosions were reported in several Ukrainian cities, including the capital Kiev.

       In his initial statement, Mr Biden condemned Russia’s actions as “unprovoked and unjustified” and promised to hold its leaders accountable.

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       The president said Mr Putin “has chosen a premeditated war that will bring a catastrophic loss of life and human suffering”.

       “Russia alone is responsible for the death and destruction this attack will bring, and the United States and its Allies and partners will respond in a united and decisive way,” he continued.

       “The world will hold Russia accountable.”

       In a subsequent statement early Thursday, Mr Biden said he had spoken to Ukrainian President Volodymyr Zelensky and “briefed him on the steps we are taking to rally international condemnation, including tonight at the United Nations Security Council”.

       “He asked me to call on the leaders of the world to speak out clearly against President Putin’s flagrant aggression, and to stand with the people of Ukraine,” the second statement read.

       “Tomorrow, I will be meeting with the Leaders of the G7, and the United States and our Allies and partners will be imposing severe sanctions on Russia.

       “We will continue to provide support and assistance to Ukraine and the Ukrainian people.”

       Shortly after the strikes began, Ukraine’s foreign minister Dmytro Kuleba said that Mr Putin had “just launched a full-scale invasion”.

       “Peaceful Ukrainian cities are under strikes. This is a war of aggression. Ukraine will defend itself and will win. The world can and must stop Putin. The time to act is now,” Mr Kuleba tweeted.

       Follow live updates on Russia’s invasion of Ukraine

       Mr Putin claimed earlier that Russia has been left with no choice but to defend itself against what he said were threats emanating from modern Ukraine.

       "Russia cannot feel safe, develop, and exist with a constant threat emanating from the territory of modern Ukraine," he said.

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       He also promised Russia would respond instantly if any external force tried to interfere and that Moscow would try to de-militarise and “de-Nazify” Ukraine.

       Reuters contributed to this report