Russia has also demanded that the United States remove all of its nuclear weapons from Europe, and that Ukraine, Belarus and Georgia, three surrounding states that once were part of the Soviet empire, never join NATO.
It is still unclear whether Mr. Putin believes those are realistic strategic objectives — Wendy R. Sherman, the deputy secretary of state, called them “nonstarters” this week — or whether his true focus is on bringing Ukraine to heel. The Russian president wants to expand his country’s sphere of influence to include more of the old Soviet bloc, especially former Soviet republics like Ukraine.
The United States has vowed both severe financial and technological sanctions if Russia invades, and it has said it would consider arming a Ukrainian insurgency to make any Russian occupation expensive and bloody. Both Defense Secretary Lloyd J. Austin III and Gen. Mark A. Milley, the chairman of the Joint Chiefs of Staff, have warned their Russian counterparts in recent telephone calls that any swift Russian victory in Ukraine would probably be followed by a bloody insurgency similar to the one that drove the Soviet Union from Afghanistan.
After the Biden administration made the new accusation against Russia, Representative Adam B. Schiff, Democrat of California and the chairman of the House Intelligence Committee, said the news underscored the need to “provide Ukraine with the defensive weapons needed to deter aggression, and, if unsuccessful at deterrence, make a Russian invasion costly to the invaders.”
The Kremlin pushed back against the intelligence assessment. “So far, all these statements have been unfounded and have not been confirmed by anything,” Dmitri S. Peskov, Mr. Putin’s spokesman, told TASS, a state-run news agency.
The intelligence finding was reported earlier by CNN.
One senior Biden administration official said there was concern that saboteurs or provocateurs could stage an incident in Kyiv, the Ukrainian capital, creating a possible pretext for a coup. President Volodymyr Zelensky of Ukraine declared several months ago that he believed a coup attempt was underway, but it never materialized.
Understand the Escalating Tensions Over Ukraine
Ominous warnings. Russia called the strike a destabilizing act that violated the cease-fire agreement, raising fears of a new intervention in Ukraine that could draw the United States and Europe into a new phase of the conflict.
The Kremlin’s position. President Vladimir V. Putin of Russia, who has increasingly portrayed NATO’s eastward expansion as an existential threat to his country, said that Moscow’s military buildup was a response to Ukraine’s deepening partnership with the alliance.
Ukraine’s military intelligence service announced earlier on Friday that it had intercepted information about a plot by Russian spies to start a sabotage operation from disputed territory in Moldova, south of Ukraine, where Russia maintains a large contingent of troops. The plan, according to the intelligence service, was to attack Russian troops stationed at a weapons depot near the border with Ukraine and blame it on Ukrainian forces.