Russia has arrested 11 people, including four suspected gunmen, in connection with a shooting rampage that killed 143 people in a concert hall near Moscow, the Kremlin said on Saturday.
It said FSB security service chief Alexander Bortnikov had reported to President Vladimir Putin that those detained included "four terrorists" and that the service was working to identify their accomplices.
Russia's Investigative Committee said the death toll had leapt to 143 from the attack in which camouflage-clad gunmen opened fire with automatic weapons at concertgoers near the capital on Friday. It said some died from gunshot wounds and others in a huge fire that broke out in the complex.
Interfax quoted the FSB security service as saying the four suspected gunmen had been arrested while heading to the Ukrainian border and that they had contacts in Ukraine. It said they were being transferred to Moscow.
Russia has not made public any evidence of a Ukrainian connection. Ukrainian presidential adviser Mykhailo Podolyak said on Friday that Kyiv had nothing to do with Friday's attack, for which Daesh (IS) claimed responsibility.
Russian lawmaker Alexander Khinshtein said the attackers had fled in a Renault vehicle that was spotted by police in the Bryansk region, about 340 km (210 miles) southwest of Moscow on Friday night and disobeyed instructions to stop.
He said two were arrested after a car chase, and two others fled into a forest. From the Kremlin account, it appeared they, too, were later detained.
Khinshtein said a pistol, a magazine for an assault rifle, and passports from Tajikistan were found in the car. Tajikistan is a Central Asian state that used to be part of the Soviet Union.
In the deadliest attack in Russia since the 2004 Beslan school siege, gunmen sprayed civilians with bullets just before Soviet-era rock group "Picnic" was to perform to a full house at the 6,200-seat Crocus City Hall just west of the capital.
A verified video showed people taking their seats in the hall, then rushing for the exits as repeated gunfire echoed above screams. Other videos showed men shooting at groups of people. Some victims lay motionless in pools of blood.
"Suddenly, there were bangs behind us - shots. A burst of firing - I do not know what," one witness, who asked not to be identified by name, told Reuters.
"A stampede began. Everyone ran to the escalator," the witness said. "Everyone was screaming; everyone was running."
Russian investigators said the death toll was more than 90. Health officials said 100 people were wounded, of which about 60 were in critical condition.
In the 2004 Beslan school siege, militants took more than 1,000 people, including hundreds of children, hostage.
Security chiefs, including Alexander Bortnikov, the head of the Federal Security Service (FSB), were updating Russian President Vladimir Putin about the situation, the Kremlin said.
Russian investigators published pictures of a Kalashnikov automatic weapon, vests with multiple spare magazines and bags of spent bullet casings.
DAESH (IS)
DaeIS (IS), the militant group that once sought control over swathes of Iraq and Syria, claimed responsibility for the attack, the group's Amaq agency said on Telegram.
A grainy picture was published by some Russian media of two of the alleged attackers in a white car.
The fate of the attackers was unclear as firefighters battled a massive blaze and emergency services evacuated hundreds of people while parts of the venue's roof collapsed.
Daesh said its fighters attacked on the outskirts of Moscow, "killing and wounding hundreds and causing great destruction to the place before they withdrew to their bases safely." The statement gave no further detail.
The United States has intelligence confirming Daesh's claim of responsibility for the shooting, a US official said on Friday. The official said Washington had warned Moscow in recent weeks of the possibility of an attack.
"We did warn the Russians appropriately," said the official, speaking on condition of anonymity without providing any additional details.
Russia has yet to say who it thinks is responsible.
The attack on Crocus City Hall, about 20 km (12 miles) from the Kremlin, comes just two weeks after the US embassy in Russia warned that "extremists" had imminent plans for an attack in Moscow.
Hours before the embassy warning, the FSB said it had foiled an attack on a Moscow synagogue by Daesh's affiliate in Afghanistan, known as Daesh Khorasan or Daesh-K, and seeks a caliphate across Afghanistan, Pakistan, Turkmenistan, Tajikistan, Uzbekistan and Iran.
Putin changed the course of the Syrian civil war by intervening in 2015, supporting President Bashar al-Assad against the opposition and Daesh.
"Daesh-K has been fixated on Russia for the past two years, frequently criticising Putin in its propaganda," said Colin Clarke of the Soufan Center.
The broader Daesh has claimed deadly attacks across the Middle East, Afghanistan, Pakistan, Iran, Europe, the Philippines and Sri Lanka.
Russian Foreign Ministry spokeswoman Maria Zakharova said it was a "bloody terrorist attack" that the entire world should condemn.
The United States, European and Arab powers and many former Soviet republics expressed shock and sent their condolences. Ukrainian presidential adviser Mykhailo Podolyak denied any Ukrainian involvement.
The United Nations Security Council condemned what it called a "heinous and cowardly terrorist attack."
SECURITY TIGHTENED
Russia tightened security at airports, transport hubs, and across the capital, a vast urban area of over 21 million people. All large-scale public events were cancelled across the country.
Putin, who was on Sunday re-elected for a new six-year term, sent thousands of troops into Ukraine in 2022 and has repeatedly warned that various powers - including countries in the West - are seeking to sow chaos inside Russia.
The Kremlin said that Putin was informed in the first minutes of the attack and is regularly being updated.
"The president constantly receives information about what is happening and the measures being taken through all relevant services. The head of state gave all the necessary instructions," Kremlin spokesperson Dmitry Peskov said.
At Crocus City Hall, flames leapt into the sky, and plumes of black smoke rose above the venue as hundreds of blue lights from emergency vehicles flashed in the night.
Helicopters sought to douse flames that engulfed the large building. The roof of the venue was collapsing, state news agency RIA said.
"A terrible tragedy occurred in the shopping centre Crocus City today," Moscow Mayor Sergei Sobyanin said. "I am sorry for the loved ones of the victims."
Russia tightened security at airports, transport hubs, and across the capital, a vast urban area of over 21 million people. All large-scale public events were cancelled across the country.
Putin, who was on Sunday re-elected for a new six-year term, sent thousands of troops into Ukraine in 2022 and has repeatedly warned that various powers - including countries in the West - are seeking to sow chaos inside Russia.