"As a result of working with detained terrorists, studying the technical devices seized from them, and analysing information about financial transactions, evidence was obtained of their connection with Ukrainian nationalists," a statement from Russia's Investigative Committee said.
It added that there was "confirmed data" that the gunmen had received significant amounts of cash and cryptocurrency from Ukraine, Reuters reports, and claimed that another suspect involved in "the terrorists' financing scheme" had been detained by officials.
White House national security spokesperson John Kirby called the allegations "nonsense and propaganda."
"In fact, the United States tried to help prevent this terrorist attack and the Kremlin knows this," he said, adding that the Islamic State (IS) was solely responsible for the attack.
The IS claimed responsibility shortly after the massacre, which left over 140 people dead, last Friday. It released a statement that read: "Islamic State fighters attacked a large gathering of Christians in the city of Krasnogorsk on the outskirts of the Russian capital, Moscow, killing and wounding hundreds and causing great destruction to the place before they withdrew to their bases safely."
Kyiv has also vehemently denied any involvement in the attack and the US has stood behind them.
Kirby stated, "We take seriously our duty to warn. We never want to see innocent lives lost in terrorist attacks," and added that Washington has passed "many warnings" to Moscow "about various threats" since September, including a written warning to Russian security services on March 7.
US officials have said they believe the Islamic State Khorasan, the network's Afghan branch, was responsible for the attack, but Russia has remained skeptical, noting that the fact the US named a potential perpetrator so quickly was suspicious.
