By James Pearson and Alexander Marrow LONDON (Reuters) -A hacking group believed by Kyiv to be affiliated with Russian military intelligence claimed responsibility on Wednesday for a cyberattack that knocked Ukraine’s biggest mobile network operator offline. Tuesday’s attack on Kyivstar, which has 24.3 million mobile subscribers and more than 1.1 million home internet users, knocked out services, damaged IT infrastructure, and silenced air raid alert systems in some parts of Ukraine. A group of activist hackers, or “hacktivists”, called Solntsepyok said in a post on the Telegram messaging app …