Jake Sullivan, President Biden’s national security adviser, said on Sunday that U.S. officials still believed that President Vladimir V. Putin of Russia could invade Ukraine at any time, despite continuing diplomatic efforts.
“The way they have built up their forces, the way they have maneuvered things in place, makes it a distinct possibility that there will be major military action very soon,” Mr. Sullivan said during an interview on CNN’s “State of the Union.”
“We are prepared to continue to work on diplomacy,” he added, “but we are also prepared to respond in a united and decisive way with our allies and partners should Russia proceed.”
Mr. Sullivan’s comments came a day after Mr. Biden spoke with Mr. Putin for more than an hour by phone. Mr. Biden, his advisers said, discussed a range of diplomatic options with the Russian president, but also warned of “swift and severe” consequences should Mr. Putin initiate a major attack on Ukraine. Officials believe Mr. Putin could first use aerial forces and bombs before ordering a ground invasion.
The two leaders spoke only hours after the United States ordered most of its diplomats and other staff members to leave the American Embassy in Ukraine. Mr. Biden and President Volodymyr Zelensky of Ukraine are scheduled to speak on Sunday morning.
Mr. Sullivan also explained why American officials were working to dispel what they believe are attempts by the Russians to justify invading. Asked about the so-called false-flag operation, he said that the world should be prepared for Russia “staging a pretext and then launching a potential military action,” and noted that the Russians had used this playbook during other conflicts.
“Our view is that we’re not going to give Russia the opportunity to conduct a surprise here — to spring something on Ukraine or the world,” Mr. Sullivan said.
But Maria Zakharova, a spokeswoman for the Russian Foreign Ministry, hit back hard at these warnings.
“The world already knows who lies all the time,” she wrote on her channel on the app Telegram and on Facebook. She invoked former Secretary of State Colin Powell’s invocation of “weapons of mass destruction” in 2003 as a pretext to invade Iraq as an example, saying “I would like to remind Mr. Sullivan of the video footage from this speech in his native language.”
“American politicians have lied, are lying and will continue to lie, creating pretexts to attack civilians around the world,” she wrote. “Everyone knows this. I would ask the American political establishment not to commit and bear another sin on their souls, but I’m not sure they have them.”
Mr. Biden has threatened to impose severe economic sanctions against Russia in the event of an invasion, and has said that the United States would restrict a controversial Germany-to-Russia gas pipeline from going forward.
On Sunday, Mr. Sullivan said officials were working to divert gas cargos to Europe if Russia “turns down the taps.” And he said that officials were working to draw up lists of people close to Mr. Putin whom the United States would penalize in the event of an invasion.
In other interviews on Sunday morning television, member of Congress weighed in on the crisis.
“If we were not threatening the sanctions and the rest, it would guarantee that Putin would invade,” Speaker Nancy Pelosi, Democrat of California, said on ABC’s “This Week.” “Let’s hope that diplomacy works. It’s about diplomacy, deterrence.”
She vowed that Congress, whose senior lawmakers have struggled to reach bipartisan agreement on a sanctions package, would be united in opposition to a Russian invasion
Senator Lindsey Graham, Republican of South Carolina, who appeared on the ABC show after Ms. Pelosi, said he believed “we can do more in Congress and should.”
“The best thing that could happen is for us to pass this sanctions package preinvasion, with a waiver,” he added, saying that the measure would “destroy the ruble and cripple the Russian economy.”
Valerie Hopkins contributed.
An earlier version of the headline with this article misidentified the country that U.S. officials still believed President Vladimir V. Putin of Russia could invade at any time. It is Ukraine, not Russia.