MOSCOW — The suicide bomber who killed 35 people and wounded 180 at Moscow’s largest airport was a 20-year-old man from the volatile southern Caucasus region, Russian investigators said Saturday.

Breaking a five-day silence over the probe, federal investigators also said foreigners were deliberately targeted, marking an ominous new tactic in Russia’s losing battle with extremism.

Islamist rebels from the Caucasus, a group of mountainous Russian provinces that are beset with an entrenched separatist insurgency, had been widely suspected in the attack at Domodedovo Airport.

Saturday’s statement from federal investigators confirmed a suicide blast involving a bomb containing shrapnel. While authorities say they know the identity of the perpetrator, they suggested they still don’t know who masterminded the attacks.