Russia has jailed the four men accused of carrying out a deadly Moscow attack on terrorism charges as the death toll climbed to 137.

The men, at least one a Tajik, were remanded in custody and face life in prison, although Russian officials have clamored for the lifting of a moratorium on the death penalty to deliver even harsher sentences.

In a series of late-night court hearings in Moscow that ran into the early hours Monday, the men – with bruises and cuts over their faces – were dragged into the court in front of dozens of reporters who had assembled at the capital's Basmanny district court.

FSB security service officers wheeled one into the hearing on a medical gurney, following reports and videos on Russian social media of bloody interrogations after the men were arrested Saturday.

Daesh has claimed responsibility for the attack, a claim that the United States has publicly said it believes, and the terrorist group has since released what it says is footage from the attack.

U.S. officials said they had warned Russia of intelligence about an imminent attack earlier this month.

Russian officials, however, have cast doubts on such claims. On Monday, Moscow challenged U.S. assertions and accused Washington of covering for Ukraine.

Although President Vladimir Putin has not publicly mentioned the terrorist group in connection with the attackers, he said claimed some people on "the Ukrainian side" had been prepared to spirit the gunmen across the border.

Ukraine has denied any role in the attack and President Volodymyr Zelenskyy has accused Putin of seeking to divert blame for the attack by mentioning Ukraine.

Russia's Foreign Ministry spokeswoman, Maria Zakharova, called into question U.S. assertions that Daesh, which once sought control over swathes of Iraq and Syria, was behind the attack.

In an article for the Komsomolskaya Pravda newspaper, she said the United States was evoking the "bogeyman" of Daesh to cover its "wards" in Kyiv and reminded readers that Washington had supported the "mujahideen" fighters who fought Soviet forces in the 1980s.

Two U.S. officials said Friday that the United States had intelligence confirming Daesh's claim of responsibility.

Battered faces

Kremlin spokesman Dmitry Peskov later told reporters that Russia could not comment on the Daesh claim while the investigation was ongoing, and would not comment on the U.S. intelligence, saying it was sensitive information.

Putin earlier said 11 people had been detained, including the four suspected gunmen, who he said had fled the concert hall and made their way to the Bryansk region, about 340 kilometers (210 miles) southwest of Moscow, to slip across the border to Ukraine.

Unverified videos of the suspects' interrogations circulated on social media. One of the suspects was shown having part of his ear cut off and stuffed into his mouth.

One man, a Tajik named Dalerdzhon Mirzoyev, leaned against the glass cage as the terrorism charge was read out. Saidakrami Rachabalizoda, his ear in bandages, remained sitting.

Muhammadsobir Fayzov appeared in gaping hospital clothes and sat in a medical chair, his face covered in cuts. Shamsiddin Fariduni, his face bruised, stood.

The Kremlin's Peskov left a journalist's question about the treatment of the detainees unanswered.