Iran had tipped off Russia about the possibility of a major "terrorist operation" on its soil ahead of the concert hall massacre near Moscow last month, three sources familiar with the matter said.

Iran alerted Russia about security threat before Moscow concert hall terror attack

The Kremlin on Thursday (Mar 28) told Telegram's owner Pavel Durov to be more attentive after the messaging platform was allegedly used to help recruit the gunmen behind the March 22 Moscow concert hall attack that killed over 140 people.

Be more attentive: Kremlin's note of caution to Telegram owner following Moscow terror attack

There has been a surge of migrant workers leaving Russia for Tajikistan after a March 22 concert hall attack near Moscow which left dozens dead, according to Tajikistan's Ministry of Labour, Migration and Employment.

Tajikistan says migrants fleeing Russia after concert hall terror attack

The former employer of Moscow concert hall terror attack suspect Muhammadsobir Fayzov said she noticed nothing strange about him. Fayzov, 19, is the youngest of suspects behind the shooting at the Crocus City Hall that killed 143 people and injured 360 others.

Moscow terror attack: Noticed nothing strange about him, says suspect's ex-employer