The final death toll from the Moscow concert hall attack last week could be higher than the 143 confirmed dead, as Russian investigators said they have received more than 100 reports of missing people.

Moscow's Basmanny District Court formally charged Dalerdzhon Mirzoyev, 32; Saidakrami Rachabalizoda, 30; Shamsidin Fariduni, 25; and Mukhammadsobir Faizov, 19, with committing a group terrorist attack resulting in the death of others. The offense carries a maximum sentence of life imprisonment.

The four suspected attackers were arrested and identified as Tajik nationals. An affiliate of the Islamic State group claimed responsibility for the attack, the deadliest on Russian soil in years. The Kremlin, however, has insisted that Ukraine and the West had a role, something Kyiv has vehemently denied.

The four men suspected of carrying out a brutal attack at a Moscow concert hall that killed at least 139 people have appeared in court on terror charges, as the Kremlin defended its security services criticized for failing to prevent the massacre.