Russians are mourning the victims of an attack at a popular concert hall in Moscow's suburbs, which killed at least 137 people, and injured more than 150 others.

Islamic State has claimed responsibility for the deadliest terror attack on Russian soil in two decades, but in his first public address President Vladimir Putin made no mention of Islamic State and suggested - without evidence - the attackers planned to flee to Ukraine.

Guest: John Sipher, retired CIA veteran who worked for the intelligence agency for 28 years, including running Russia operations in Moscow