Russia marked a day of mourning on Sunday, two days after a deadly attack on a suburban Moscow concert hall killed 137 people, including three children, and injured more than 180.

Rescue teams continued to search for survivors in charred buildings, and some families were still grieving over the fate of their loved ones. Russia’s health ministry said hundreds of people lined up in Moscow to donate blood and plasma.

Friday’s attack was the worst on Russian soil since the 2004 Beslan school siege, when Islamist militants took more than 1,000 people, including hundreds of children, hostage.

On Friday, four armed men walked up to a metal detector at Crocus City Hall, a 6,200-seat concert hall outside Moscow, and fired automatic weapons at the crowd, witnesses said. A hail of bullets fired at short range as panicked civilians screamed and fell.

The terrorist group Islamic State claimed responsibility for Friday’s attack.

IS said in a statement posted on Telegram by its affiliate Aamaq news agency that it attacked a large rally in the Moscow suburb of Krasnogorsk, killing and injuring hundreds of people. The veracity of that claim could not immediately be verified.

IS released a grainy video purportedly showing gunmen storming what appeared to be the Crocus concert hall.

Russian President Vladimir Putin delivered a televised address to the nation on Saturday, expressing his “deepest condolences” to the families of the victims and declaring a national day of mourning. He vowed to track down and punish all those behind what he called a “bloody, brutal” attack. A barbaric act of terror. He said 11 people, including four gunmen, had been detained after they fled the concert hall and headed for the Bryansk region, about 340 kilometers (210 miles) southwest of Moscow.

“They tried to hide and go to Ukraine, and according to preliminary data, a window was prepared for them on the Ukrainian side to cross the state border,” Putin said.

Russia’s Federal Security Service (FSB) claimed the gunman had ties to Ukraine and was captured near the border.

Ukrainian President Volodymyr Zelensky dismissed Putin’s claims that Ukraine was involved in a speech on Saturday night.

“Putin and other scumbags just want to blame someone else,” he said.

The White House said on Sunday that Ukraine had “no involvement” in the massacre at a Moscow concert hall that left more than 137 people dead, the White House said on Sunday after Putin hinted at ties to Kiev.

“Islamic State bears full responsibility for this attack. Ukraine had no involvement,” White House National Security Council spokesperson Adrienne Watson said, using an abbreviation for the group. U.S. officials said the Islamic State’s Afghan affiliate, the Islamic Khorasan Group, carried out the attack.

The White House said the U.S. government shared information with Russia earlier this month about Moscow’s planned attacks and issued a public warning to Americans in Russia on March 7. Earlier this week, Putin denounced the U.S. warning as an attempt to intimidate Russians.

In video footage posted by Russian media and Telegram channels close to the Kremlin, one of the arrested suspects said he was offered money to carry out the attack.

“I shot people,” the suspect said on camera, his hands tied, his hair grabbed by the interrogator and black boots under his chin.

Another suspect was answering questions through a Tajik translator.

Tajik President Emomali Rahmon condemned the Moscow concert hall attack in a phone call with Putin on Sunday and accused the gunman of being a Tajik citizen, the Moscow Times reported.

The Islamic State (IS) organization is very active in Tajikistan. This Central Asian country borders Afghanistan.

The Kremlin said on Sunday that Putin and Emomali Rahmon had agreed to “step up” joint counterterrorism efforts.

Flags in Russia were flown at half-mast on Sunday and television entertainment and advertising were suspended, state news agency RIA Novosti reported.

People laid flowers at a makeshift memorial near the charred concert hall.

On March 7, just hours before the U.S. Embassy warned of an imminent attack on Russian soil, Russia’s top security agency said it foiled an Islamic State attack on a synagogue in Moscow and an attack near the Russian border. Several members of the group were killed in the Kaluga region. capital.

Days earlier, Russian authorities said six suspected Islamic State members had been killed in a shootout in Ingushetia, Russia’s Caucasus region.

Some of the information in this report was provided by The Associated Press, AFP and Reuters.