Outside the burnt-out Crocus City Concert Hall is a growing collection of flowers, hand-written notes and other tributes
Outside the burnt-out Crocus City Concert Hall is a growing collection of flowers, hand-written notes and other tributes AFP

Russian officials said Friday they had arrested three people plotting an attack in the country's south, a week after the assault on a Moscow concert hall killed at least 144 people.

The FSB security agency said it had "put an end to the terrorist activities of three nationals from a Central Asian country", Russian news agencies reported.

The three suspects had been "planning to commit a terrorist act by blowing up a device in a public place in the Stavropol region", it added.

Russian television showed images of several men pinned to the ground by FSB agents.

The RIA Novosti news agency said the ingredients for an improvised explosive device (IED) and chemical substances had been found at the home of one of the suspects.

The Stavropol region sits in the North Caucasus region of southern Russia, bordering Dagestan and Chechnya among others.

The announcement came a week after the massacre at the Crocus City concert hall on the outskirts of Moscow, which claimed at least 144 lives.

A week on, the Kremlin has acknowledged "radical Islamists" carried out the carnage, arresting 12 people including the four alleged attackers from Tajikistan.

But it has directed much of its anger at arch-foe Ukraine, insisting that Kyiv was intimately involved in the attack, while providing no evidence.

Kyiv and its Western allies have dismissed the accusations as absurd.

And the United States has pointed out that weeks before last Friday's assault it had issued a warning that extremists planned to attack mass gatherings, including concerts, in Russia.

The Kremlin has nevertheless expressed full confidence in its security services, despite criticism over their failure to thwart the attack.

Earlier Friday, a Russian court ordered the pre-trial detention of another suspect in last week's attack.

Nine of the 12 people have already been sent to pre-trial detention, but there has been no update on the other three.

The Islamic State (IS) group has repeatedly claimed responsibility for the attack, its deadliest on European soil.

But Russian President Vladimir Putin has alleged a Ukrainian and Western connection.

Russia's Investigative Committee has said it has evidence that "Ukrainian nationalists" were behind the attack and had funded the gunmen with cryptocurrency payments from Ukraine.

It did not provide details of the allegations.