© Sputnik / Yekaterina Shtukina
The perpetrators and masterminds of Friday's deadly terrorist attack at a Moscow concert venue must be killed without mercy, former Russian President Dmitry Medvedev has claimed.

At least 137 people have been killed and over 180 were wounded when several men armed with assault rifles opened fire inside the Crocus City Hall and then proceeded to set the concert venue ablaze. Four men suspected of carrying out the attack have been captured. Two of them have confessed in court, and are set to remain in custody until late May. They all face life in prison.

"Everyone asks me. What to do? ... Should they be killed?" wrote Medvedev, currently deputy chair of the National Security Council, in a Telegram post on Monday.

"It should and will be done," he stressed, adding: "It is much more important to kill everyone involved. Everyone. Who paid, who sympathized, who helped. Kill them all."

Medvedev earlier stated that "Terrorists understand only terror in response" and that "all of them must be found and mercilessly destroyed as terrorists - including officials of the state that committed such an atrocity."

The former Russian president vowed to "avenge each and every" victim of the Crocus City Hall attack, regardless of country of origin and status, insisting this "is now our legal and main goal."

Medvedev's comments come amid growing calls among the country's lawmakers to restore the death penalty, which has effectively been banned in Russia since 1996. While the Russian criminal code technically has a provision for capital punishment, courts are de facto banned from handing down such a sentence.