Russia’s internal security chief has accused Britain and the United States of being behind Friday’s terrorist attack on Crocus City Hall.

Alexander Bortnikov, the head of the Federal Security Service, the main successor to the KGB, said investigators had not yet established who ordered the attack but insisted the West and Ukraine were linked to it.

“We believe the action was prepared both by the radical Islamists themselves and, of course, facilitated by Western special services, and Ukraine’s special services themselves have a direct connection to this,” Mr Bortnikov was cited as saying by Russian news agencies.

“The one who ordered it has not been identified yet. We understand and see those who organised this process, who recruited and set specific tasks,” he said.

However Mr Bortnikov went on to declare: “The USA, Britain and Ukraine are behind the terrorist attack in Crocus City Hall.”

At least 139 people were murdered in the attack on the concert venue outside Moscow on Friday evening. The Islamic State terrorist group has claimed responsibility.

Mr Bortnikov’s remarks come after Vladimir Putin on Monday for the first time publicly accepted that Islamist extremists perpetrated the attack but insisted there was some link to Ukraine.

The FSB has previously said the suspected attackers were caught in Bryansk region on their way to the Ukrainian border. Mr Bortnikov claimed they would have been “greeted as heroes on the other side” if they had made it.

Ukraine has strongly denied any involvement in the atrocity.

The United States, which says it shared intelligence about a possible terror attack in Moscow with Russia, says its intelligence shows Islamic State operatives acted alone.

Mr Bornikov’s comments came as Russian authorities arrested an eighth man in connection with the Crocus City Hall terrorist attack.

Alisher Kasimov, a Russian citizen born in Kyrgyzstan, is accused of renting a flat to the attackers, Russian media reported. He said in court on Tuesday morning he did not know of their plans.

Officials said he was ordered to be held in detention until at least May 22, without detailing the exact accusations against him.

The four suspected attackers were detained on Saturday after several hours on the run.

Dalerdzhon Mirzoyev, 32; Saidakrami Rachabalizoda, 30; Shamsidin Fariduni, 25; and Mukhammadsobir Faizov, 19 have been remanded in custody until May 22.

All four showed signs of beatings and torture when they were arraigned in court over the weekend. Footage released on Wagner-affiliated Telegram channels showed security officers electrocuting one of the men with a field telephone wired to his genitals. Another video showed an officer cutting off Rachabalizod’s right ear and pushing it into his mouth.

Three other men, all from the same family, were arrested on Monday evening on suspicion of assisting the attackers by providing the getaway vehicle.

Brothers Dilovar and Aminchon Islomov have been charged with terrorism. Their father Isroil Islomov has not been charged but is considered a suspect, Meduza reported.

Alexander Bastrykin, the head of Russia’s investigative committee, said on Monday that the three, who live in the city of Tver northwest of Moscow, were believed to be part of the terrorist group and assisted the attackers by providing the vehicle, a flat, and moving money for them.

Dilovar Islomov told Novaya Gazeta Europe that he and his brother turned themselves in when they recognised the white Renault used by the attackers as the car he had sold to his wife’s brother a week previously. He said they were innocent of involvement in the terror attack.

‘Attackers’ travelled between Russia and Turkey

The arrests came as further details emerged of the suspected attackers movements before Friday night.

At least two of the alleged attackers had recently travelled between Russia and Turkey.

A Turkish official told the AFP news agency that Saidakrami and Fariduni “were able to travel freely between Russia and Turkey since there was no warrant for their arrest”.

The attack has prompted calls in Russia for a review of its three-year moratorium on the death penalty.

Those calls gathered steam on Tuesday when Vyacheslav Volodin, the speaker of the State Duma, Russia’s lower house of parliament, said that a cross-party committee should be formed to examine the question. He added that restoring the death penalty would require a decision of the Constitutional Court, but not a referendum on changing the law.