The US repeatedly alerted Russia that extremists were planning to attack large gatherings in Moscow ahead of last week’s concert hall attack that claimed more than 140 lives, the White House has said. The national security spokesperson, John Kirby, said on Thursday that US officials passed on warnings – including one in writing – and dismissed Russian allegations that Ukraine was involved as “nonsense”. “It is abundantly clear that Isis [Islamic State] was solely responsible for the horrific attack in Moscow last week,” he 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. “As a result of work with the detained terrorists, examination of the technical devices seized from them and analysis of information on financial transactions, evidence of their links with Ukrainian nationalists has been obtained,” Russia’s investigative committee said on Thursday. It alleged the suspects had received “significant amounts of money and cryptocurrency from Ukraine” and said another man “involved in financing the terrorists” had been identified and detained. “Investigators will ask the court to remand him in custody,” it said. Kirby described the Russian allegations of Ukrainian involvement as “nonsense and propaganda”. Kirby said that the US provided several advance warnings to Russian authorities of extremist attacks on concerts and large gatherings in Moscow, including in writing on 7 March at 11.15am. 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. The four suspected assailants appeared in a Moscow courtroom on Sunday with bruises and cuts on their swollen faces. All four are from Tajikistan. Russia’s FSB security service said it arrested the gunmen while they were trying to flee to Ukraine, a claim seemingly disputed by the Belarusian strongman Alexander Lukashenko, who said they were headed for his country first. Islamic State jihadists have said several times since Friday that they were responsible, and IS-affiliated media channels have published graphic videos of the gunmen inside the venue. Vladimir Putin has not visited the scene of the massacre or publicly met any victims. “If any contacts are necessary, we will inform you accordingly,” the Kremlin spokesman, Dmitry Peskov, said on Thursday, when asked if Putin planned to meet family members of the dead. He also said Putin did not plan to visit Crocus City Hall, where rescuers had for the past week been searching the rubble for bodies. “In these days it would be completely inappropriate to carry out any fact-finding trips, because this would simply interfere with the work,” he said.