Moscow attack reveals ISIS-K's widening strategy of deadly disruption

ISLAMABAD -- The bloody siege at a Moscow theater on Friday underlines the expanding reach of Islamic State's Afghanistan affiliate, blamed for Russia's deadliest terror attack in two decades.

While IS claimed responsibility for the barrage of gunfire and violence that left at least 139 dead, U.S. intelligence officials and experts point the finger at ISIS-Khorasan or ISIS-K. Russian authorities have arrested four militants from Tajikistan, a mainly Muslim central Asian state known as a recruiting ground for the group.