Russian President Vladimir Putin has concluded "radical Islamists" were behind an attack on a concert hall near Moscow. He had ignored evidence about the Islamic State and tried to blame Ukraine. He admitted on Monday that the group was responsible, but he wants to know who ordered the assault.

Russians are mourning the 139 people killed on Friday night in Krasnogorsk, a city on the outskirts of the capital. It was the deadliest attack in Russia in decades. The Islamic State claimed responsibility within hours. But investigators have been sifting through the evidence and want to reach their own conclusions.

Four men from Tajikistan appeared in court on Sunday to face charges of terrorism. They had cuts and bruises and showed other signs of having been beaten. Authorities said they had also detained seven other suspects.

Putin had said the gunmen were captured as they were trying to escape to Ukraine. He met on Monday with members of his security council. He said they know who committed the crime but are interested in who benefits. "We see that the United States, through various channels, is trying to convince its satellites and other countries that, according to its intelligence, none of Kyiv's fingerprints are on the terrorist attack," he said.

US officials had dismissed Putin's claims pointing to Ukraine, saying there was "no linkage." Ukrainian leaders have denied any responsibility. They said Putin just wants to divert blame.