White House National Security Council spokesperson John Kirby has said the "images of the attack were just horrible and just hard to watch". At least 40 people have been killed and more than 140 wounded, according to unofficial reports, in the worst terror attack in Russia in years, as gunmen in combat fatigues opened fire and detonated explosives in a major concert hall on the outskirts of Moscow. At least 40 killed and more than 140 wounded in Moscow concert hall attack Moscow concert hall attack: Islamic State claims responsibility as manhunt under way after dozens died – latest updates Moscow concert hall attack: what we know so far