The United States has sent Russian security agencies a written warning about the possibility of an extremist attack during large gatherings in Moscow, White House National Security Press Secretary John Kirby revealed.

Meanwhile, John Kirby dismissed as “nonsense” Russia’s accusation that Ukraine was involved in last week’s Crocus City concert hall attack, saying it was clear that Islamic State was “solely responsible”.

Kirby made the remarks 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 claims as “nonsense and propaganda”.

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

“It is abundantly clear that the 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 that.”