Russia's commissioner for human rights has called the use of torture against detainees unacceptable, the TASS news agency reported on Tuesday.

She was speaking after the publication of videos showing the interrogation of suspects in last week's attack at the Crocus City concert hall near Moscow that killed at least 139 people and was claimed by Islamic State.

One of the suspected gunmen had part of his ear cut off during questioning, and all four bore visible injuries when they appeared at a Moscow court on Sunday. The Kremlin declined to comment on Monday when asked if they had been tortured.

"Despite the fact that the detention of criminals can be very critical, and criminal law stipulates that actions taken during arrests which cause harm do not entail liability, it is absolutely unacceptable to use torture on detainees and defendants," the commissioner, Tatyana Moskalkova, was quoted as saying by TASS.

She added that any procedural and operational actions must be carried out in accordance with the law.

The Russian constitution outlaws torture, and Russia is also part of the United Nations Convention Against Torture. REUTERS