CNN  — 

The US warned Moscow that ISIS militants were determined to target Russia in the days before assailants stormed the Crocus City Hall in an attack that killed scores of people, but President Vladimir Putin rejected the advice as “provocative.”

Gunmen stormed the concert hall near Moscow on Friday, opening fire and throwing an incendiary device in the worst terrorist attack on the Russian capital in decades.

Isis has claimed responsibility for the attack.

Experts said the scale of the carnage – some of which was captured in video footage obtained by CNN showing crowds of people cowering behind cushioned seats as gunshots echoed in the vast hall – would be deeply embarrassing for the Russian leader, who had championed a message of national security just a week earlier when winning the country’s stage-managed election.

Not only had Russian intelligence services failed to prevent the attack, they said, but Putin had failed to heed warnings from the United States that extremists were plotting to target Moscow.

Earlier this month, the US embassy in Russia had said it was “monitoring reports that extremists have imminent plans to target large gatherings in Moscow,” including concerts, and it warned US citizens to avoid such places.

US National Security Council spokesperson Adrienne Watson said the US government had “shared this information with Russian authorities in accordance with its longstanding ‘duty to warn’ policy.”

But in a speech Tuesday, Putin had blasted the American warnings as “provocative,” saying “these actions resemble outright blackmail and the intention to intimidate and destabilize?our society.”

That stance came despite Russian authorities having reported several ISIS-related incidents within the past month.

The state-run RIA Novosti reported on March 3 that six ISIS members were killed in a counter-terrorist operation in the Ingush Karabulak; on March 7, it said security services had uncovered and “neutralized” a cell of the banned organization Vilayat Khorasan in the Kaluga region, whose members were planning an attack on a synagogue in Moscow; and on March 20, it said the commander of an ISIS combat group had been detained.

Two sources familiar with the American information said that since November there had been a steady stream of intelligence that ISIS-K – an affiliate of ISIS that is active in Afghanistan and the surrounding region – was determined to attack Russia.

Moscow has intervened tellingly in Syria’s civil war, to the support of President Bashar al-Assad and against ISIS.

ISIS-K “sees Russia as being complicit in activities that regularly oppress Muslims,” Michael Kugelman of the Washington-based Wilson Center said, as quoted by Reuters.

He added that the group also counts as members a number of Central Asian militants, who hold?their own grievances against Moscow.

A US official said Friday that Washington had no reason to doubt ISIS’ claim that it was responsible for the latest attack.

On Friday, following reports of the Crocus City Hall attack, the US embassy advised US citizens not to travel to Russia.