President Vladimir Putin on Monday night said for the first time that "radical Islamists" were behind Friday's attack on a concert hall outside Moscow, but otherwise doubled down on his previous claim that Ukraine may have somehow been involved and suggested that Washington was allegedly trying to cover it up.Eleven people were detained on Saturday in connection with the previous night's attack, which saw camouflaged gunmen storm into the popular music venue Crocus City Hall, open fire on concert-goers and set the building ablaze, killing at least 139 people and wounding 182 others"We know that the crime was committed by radical Islamists, whose ideology the Islamic world has itself been fighting for centuries," Putin said in a televised meeting with top government officials."We also see that the United States by various means is trying to convince its satellites, as well as other countries, that according to their intelligence information, there was allegedly no trace of Kyiv's [involvement] in the Moscow terrorist attack," he continued."This atrocity may be just one link in a whole series of attempts by those who have been at war with our country since 2014," Putin said, referring to Ukraine as a "neo-Nazi regime.""Of course, it is necessary to answer the question, why after committing the crime did the terrorists then try to go to Ukraine? Who was waiting for them there?"Putin had claimed before that the gunmen behind Friday's attack had driven their getaway car toward the Ukrainian border before being detained the following morning.The Islamic State’s affiliate ISIS-K has claimed responsibility for the attack, the deadliest in Russia since the 2003 Beslan school siege, and social media channels linked to the militant group have published graphic videos of the gunmen committing the mass killing at Crocus City Hall.Earlier on Monday, Kremlin spokesman Dmitry Peskov had declined to comment on the apparent link between the Islamic State and the concert attack.