Russian President Vladimir Putin has suggested that Ukraine was linked to the attack on a concert hall on the outskirts of Moscow that killed 133 people.
The so-called Islamic State group’s (IS) Afghanistan branch claimed responsibility for Friday’s assault on the Crocus City Hall in a statement posted on social media.
A US intelligence official told the Associated Press that American agencies had confirmed that the group was responsible for the attack.
Today, Russian officials raised the death toll to 133.
In an address to the nation, Mr Putin called the attack “a bloody, barbaric terrorist act” and said all four people who were directly involved had been taken into custody.
He suggested they had been trying to cross the border into Ukraine which, he said, tried to create a “window” to help them escape.
Mr Putin said additional security measures have been imposed throughout the country and declared that Sunday will be a nationwide day of mourning.
The attack was the deadliest in Russia in years and left the concert hall a smouldering ruin.
The venue had a capacity of more than 6,000 people in Krasnogorsk, on Moscow’s western edge.
Ukraine has strongly denied any involvement in the attack.
Some Russian legislators pointed the finger at Ukraine immediately after the attack. But Mykhailo Podolyak, an adviser to Ukrainian President Volodymyr Zelensky, denied any involvement.
“Ukraine has never resorted to the use of terrorist methods,” he posted on X, formerly Twitter.
“Everything in this war will be decided only on the battlefield.”
Ukraine’s foreign ministry also denied that the country had any involvement and accused Moscow of using the attack to try to stoke fervour for its war efforts.
“We consider such accusations to be a planned provocation by the Kremlin to further fuel anti-Ukrainian hysteria in Russian society, create conditions for increased mobilisation of Russian citizens to participate in the criminal aggression against our country and discredit Ukraine in the eyes of the international community,” an official said in a statement.
Images shared by Russian state media showed a fleet of emergency vehicles still gathered outside the ruins of Crocus City Hall.
Videos posted online showed gunmen in the venue shooting civilians at point-blank range.
Russian news reports cited authorities and witnesses as saying the attackers threw explosive devices that started the fire. The roof of the theatre, where crowds had gathered for a performance by the Russian rock band Picnic, collapsed early on Saturday as firefighters spent hours fighting the blaze.
In a statement posted by its Aamaq news agency, the IS’s Afghanistan affiliate said it had attacked a large gathering of “Christians” in Krasnogorsk.
A US intelligence official told the AP that American intelligence agencies had gathered information in recent weeks that the IS branch was planning an attack in Moscow, and that US officials had privately shared the intelligence earlier this month with Russian officials.
Messages of outrage, shock and support for the victims and their families have streamed in from around the world.
On Friday, the UN Security Council condemned “the heinous and cowardly terrorist attack” and underlined the need for the perpetrators to be held accountable.
UN Secretary-General Antonio Guterres also condemned the terrorist attack “in the strongest possible terms”, his spokesman said.
Meanwhile, hundreds of people queued up on Saturday in Moscow to donate blood and plasma, Russia’s health ministry said.
Mr Putin, who extended his grip on Russia for another six years in this week’s presidential vote after a sweeping crackdown on dissent, had publicly denounced the Western warnings of a potential terrorist attack as an attempt to intimidate Russians.
“All that resembles open blackmail and an attempt to frighten and destabilise our society,” he said earlier this week.
In October 2015, a bomb planted by IS downed a Russian passenger plane over Sinai, killing all 224 people on board, most of them Russian vacation-goers returning from Egypt.
The group, which operates mainly in Syria and Iraq but also in Afghanistan and Africa, also has claimed several attacks in Russia’s volatile Caucasus and other regions in the past years. It recruited fighters from Russia and other parts of the former Soviet Union.