Russian President Vladimir Putin dismissed the warning as “provocative” fearmongering from the West.
The Kremlin has also suggested that it is open to an exchange involving Evan Gershkovich, who has been detained in Russia since March.
Valery Gerasimov, Russia's top general, has not appeared in public or on state TV since the aborted mutiny on Saturday.
Imprisoned Russian opposition leader Alexei Navalny has released excerpts of his correspondence with prison administrators, detailing sarcastic demands.
"The United States had nothing to do with this,” said John Kirby, the National Security Council coordinator for strategic communications.
Some took advantage of Elon Musk's new Twitter policies to increase their reach and promote Moscow-approved talking points.
Former arms dealer Viktor Bout, who was released from a U.S. prison in December after a swap for WNBA star Brittney Griner, started exhibiting his artworks on Tuesday.
He complained stories about the Kremlin's effort to help him win in 2016 "libel" him.
Russian-installed authorities have urged all residents of the southern Ukrainian city of Kherson to leave immediately ahead of an expected Ukrainian advance.
Pro-Kremlin officials are blaming Ukraine for a rocket attack that struck the mayor’s office in a key Ukrainian city controlled by the separatists.