The White House on Tuesday accused Russia of planning to annex more areas of eastern Ukraine through the same "annexation playbook" it used when it seized control of Crimea in 2014.
National Security Council spokesman John Kirby said Moscow was preparing to install proxy officials, establish the rouble as the default currency and force residents to apply for citizenship.
"Russia is laying the groundwork to annex Ukrainian territory that it controls in direct violation of Ukraine sovereignty," Mr Kirby said. "We know their next moves."
He said Russia's actions were a "gross violation of the UN charter".
"We will not allow it to go unchallenged or unpunished," Mr Kirby said,.
He said the American response would include further sanctions imposed on Russia.
Mr Kirby also said that more US military aid for Ukraine would be announced this week as part of another security package, including more high-mobility artillery rocket systems.
Russia invaded Ukraine on February 24 in what it calls a "special military operation".
Mr Kirby said Moscow's annexation plans include Russian holding regional referendums on joining Russia, which would be used as "basis to try to claim annexation of sovereign Ukrainian territory."
Next steps involve introducing branches of Russian banks and using the rouble as its default currency, taking control of broadcasting towers and controlling internet access, and imposing Russian citizenship on locals.
"We will never recognise any purportedly annexed territories belonging to Russia," Mr Kirby said.
He said that the White House believed Ukraine would fight these annexation attempts and that its military would try to retake the territory.
"They absolutely have a right to go on the counter-offensive inside their own country against Russian forces," Mr Kirby said.
He said Washington was hoping for a UN-led agreement between Turkey, Ukraine and Russia on lifting a Black Sea blockade to ensure the global export of grain.
On a reported sale of armed drones from Iran to Russia, he said that the US was "watching this closely and we're taking it seriously".
Ukraine's first lady, Olena Zelenska, was welcomed by US President Joe Biden and his wife Jill at the White House as part of her trip this week, which included a meeting with Secretary of State Antony Blinken.
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US President Joe Biden and US first lady Jill Biden welcome Ukrainian first lady Olena Zelenska and Ukrainian ambassador to the US Oksana Markarova at the White House in Washington. Reuters -
US President Joe Biden and US first lady Jill Biden wait to welcome Ukrainian first lady Olena Zelenska to the White House in Washington. AFP -
US President Joe Biden and US first lady Jill Biden welcomes Ukrainian first lady Olena Zelenska to the White House. AFP -
President Joe Biden and first lady Jill Biden, greet Olena Zelenska, spouse of Ukrainian's President Volodymyr Zelenskyy and Ukraine's Ambassador to the US, Oksana Markarova, left, at the White House in Washington. AP -
US President Joe Biden welcomes Ukrainian first lady Olena Zelenska at the White House in Washington. US -
US first lady Jill Biden, second left, greets Olena Zelenska, spouse of Ukrainian's President Volodymyr Zelenskyy, second right, in the Blue Room at the White House in Washington. AP -
US first lady Jill Biden meets with Ukrainian first lady Olena Zelenska at the White House in Washington. Reuters -
Ukrainian first lady Olena Zelenska (R), with US House Speaker Nancy Pelosi, arrives to speak to members of the US Congress in Washington. EPA -
Ukrainian first lady Olena Zelenska attends a meeting with members of the United States Congress, on Capitol Hill in Washington. Reuters -
Ukrainian first lady Olena Zelenska speaks to members of the US Congress about Russia's invasion of Ukraine, in the US Capitol Visitors Center Auditorium, in Washington. AFP -
Olena Zelenska, Ukraine's first lady, asked US lawmakers for more weapons during an address to Congress. AFP -
First lady of Ukraine Olena Zelenska gives an address to members of the United States Congress, on Capitol Hill in Washington. EPA -
First Lady of Ukraine Olena Zelenska (C) greets members of US Congress after giving an address in Washington. AFP -
Olena Zelenska, the first lady of Ukraine, tours the Victims of Communism Museum with Andrew Bremberg, President and CEO of the Victims of Communism Memorial Foundation, left. AP -
Olena Zelenska, spouse of Ukrainian's President Volodymyr Zelenskyy, accepts the Dissident Human Rights Award on behalf of the people of Ukraine for their fight against Russia from Dr. Edwin Feulner chairman of the Victims of Communism Memorial Foundation, at the Victims of Communism Museum in Washington. AP -
Olena Zelenska, wife of Ukraine's President Volodymyr Zelenskyy speaks with Ukrainian Ambassador to the US Oksana Markarova, after attending a meeting at the US Agency for International Development building in Washington. Reuters -
Ukraine first lady Olena Zelenska walks out of the State Departmen in Washington after meeting with Secretary of State Antony Blinken in a closed-to-press meeting. AP
