From the article:

The official said U.S. intelligence agencies had gathered information in recent weeks that the IS branch was planning an attack in Moscow. He said U.S. officials privately shared the intelligence earlier this month with Russian officials. The official was briefed on the matter but was not authorized to publicly discuss the intelligence information and spoke to the AP on condition of anonymity.

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The Kremlin didn’t immediately blame anyone for the attack, but some Russian lawmakers were quick to accuse Ukraine and called for ramping up strikes. Hours before the attack, the Russian military l aunched (sic) a sweeping barrage on Ukraine’s power system, crippling the country’s biggest hydroelectric plant and other energy facilities and leaving more than a million people without electricity.

Dmitry Medvedev, deputy head of Russia’s Security Council, said that if Ukraine involvement was proven, all those involved “must be tracked down and killed without mercy, including officials of the state that committed such outrage.”

Mykhailo Podolyak, an adviser to Ukrainian President Volodymyr Zelenskyy, denied Ukraine involvement.