MOSCOW - The Kremlin said on Monday it was not taking part in discussions about restoring the death penalty, broached by top allies of President Vladimir Putin in the wake of the Russia's deadliest attack in two decades.

Gunmen men burst into the Crocus City Hall concert venue near Moscow on Friday, killing at least 137 people and wounding 182 - the worst loss of civilian life in Russia since the 2004 Beslan school siege.

Russia has detained four men, at least one a Tajik national, who it says directly carried out the attack. The Islamic State militant group has claimed responsibility.

"Now many people are asking questions about the death penalty. This topic, of course, will be deeply, professionally, meaningfully studied," Vladimir Vasilyev, parliamentary leader of the United Russia faction in the lower house of parliament, was quoted by the state news agency TASS media as saying on Saturday.

Dmitry Medvedev, a Putin ally who served a term as Russia's president and has become stridently hawkish since Russia sent its troops into Ukraine two years ago, discussed the detained suspects on his Telegram channel on Monday.

"Do they have to be killed?" he asked. "They have to be. And will be."

The Kremlin said it would not participate in conversations about lifting the moratorium on the death penalty.

"We are not taking part in this discussion at the moment," Kremlin spokesman Dmitry Peskov told reporters at a daily briefing.

Capital punishment is legal in Russia but no executions have been carried out since 1996, when President Boris Yeltsin issued a decree establishing a de-facto moratorium, which was explicitly confirmed by the Constitutional Court in 1999.

Russia's penal code currently allows for the death penalty for five offences: murder, genocide, and attempted murder of either a judge, police officer or state official. REUTERS