Russian investigators said Thursday they had found proof that gunmen who killed over 140 people at a concert last week were linked to “Ukrainian nationalists“, an assertion dismissed by the US. Russia’s Investigative Committee said there was “confirmed data” that the attackers had received significant amounts of cash and cryptocurrency from Ukraine.Minutes later, White House national security spokesman John Kirby described the Russian claim as “nonsense” and said that Islamic State was solely responsible. The US had publicly warned earlier in March that it had intelligence that “extremists” were planning an imminent attack in Moscow. Kirby said it also provided written warning to Russian security services.