The Islamic State bears sole responsibility for the deadly concert attack, says a US national security council spokesperson.
Adrienne Watson said Ukraine had no involvement.
Vladimir Putin earlier claimed the attackers were heading towards Ukraine when they were detained, and that a "window" had been prepared for them to cross the border - without providing evidence.
"ISIS bears sole responsibility for this attack. There was no Ukrainian involvement whatsoever," said Ms Watson.
The US government shared information with Russia early this month about a planned attack in Moscow and also issued a public advisory to Americans in Russia on 7 March, she said.
