Russian authorities detained 11 people, state media reported on Saturday, after gunmen stormed a concert hall in Moscow in a grisly attack that left at least 133 people dead. Russia’s Investigative Committee said four of those detained were directly involved in the attack that left the sprawling shopping mall and music venue smouldering with a collapsed roof. A US intelligence official said that US agencies had confirmed that the ISIS group was responsible for the attack. 

The Islamic State group claimed responsibility for the attack in a statement posted on affiliated channels on social media. A US intelligence official said that US intelligence agencies had learned the group’s branch in Afghanistan was planning an attack in Moscow and shared the information with Russian officials. The four suspects were stopped in the Bryansk region of western Russia, “not far from the border with Ukraine,” Russia’s Investigative Committee said. They planned to cross the border into Ukraine and “had contacts” there, state news agency Tass said, citing Russia’s FSB. The head of the FSB briefed President Vladimir Putin on the arrests on Saturday, according to Tass.