In a briefing to reporters, White House national security spokesman John Kirby said that the United States passed to Russian security services a written warning of an extremist attack on large gatherings in Moscow, one of many provided in advance.

"It is abundantly clear that ISIS (Islamic State) was solely responsible for the horrific attack in Moscow last week," Kirby said. "In fact, the United States tried to help prevent this terrorist attack and the Kremlin knows this."

Kirby spoke shortly after Russia's Investigative Committee said it had uncovered evidence that the four gunmen who carried out last Friday's attack were linked to "Ukrainian nationalists" and had received cash and cryptocurrency from Ukraine.

He described the Russian allegations as "nonsense and propaganda."

The United States, he said, provided multiple advance warnings to Russian authorities of extremist attacks on concerts and large gatherings in Moscow, including in writing on March 7 at 11:15 am, to Russia's security services.

The United States passed "following normal procedures and through established channels that have been employed many times previously...a warning in writing to Russian security services," Kirby said.

(Reporting by Jonathan Landay, Jarrett Renshaw and Rami Ayyub; Editing by Chizu Nomiyama)