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

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 that "radical Islamists" carried out the carnage, arresting 12 people including the four attackers from Tajikistan.

But it has directed much of its anger at Ukraine, insisting that Kiev was involved in 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) terrorist group has repeatedly claimed responsibility for the attack, its deadliest on European soil.

But 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.