A disturbing video circulating on Russian social media shows members of the country's security forces cutting off the ear of a man who is later interrogated over the terror attack in Moscow yesterday.

The Crocus City Hall attack killed at least 133 people and wounded more than 100, making it the deadliest attack in Russia since the Beslan school siege 20 years ago.

Gunmen attacked the packed concert venue on the outskirts of Russia's capital, in what the Russian security service called a "carefully planned" assault.

Russian state news aired footage of interrogations of three alleged attackers in Bryansk, close to the Ukrainian and Belarusian border in western Russia.

One of the suspects explains that he arrived in Russia from Turkey and was to receive 500,000 rubles (£4,300) for the attack.

He can be heard telling the Russian officers: "They told me to go and kill people, no matter what kind."

Another suspect speaks in Tajik through an interpreter.

Russia’s interior ministry later confirmed that the four suspected gunmen were all foreign citizens,

ISIS-K, a group that seeks to create a caliphate across Afghanistan, Pakistan, Turkmenistan, Tajikistan, Uzbekistan and Iran, has claimed responsibility for the attack.

The Islamic terror group has previously recruited from central Asia, including Tajikistan.

Meanwhile, President Putin declared a day of mourning for Sunday and passed his condolences on to the families of those killed in the attack.