United Nations Secretary-General Ban Ki-moon has condemned the alleged attack on a Russian plane in "the strongest terms" and voiced his deep sadness for the victims of the crash in Egypt's Sinai earlier on Saturday.Ban told a group of journalists here on Saturday afternoon that he has received the report that the Islamic State (IS) claimed responsibility for the crash of a Russian plane, saying it is a complete crime to target civilian airlines and a full investigation should be carried out as soon as possible."I'd like to take this opportunity to offer my deep condolences to the families and loved ones of the victims and countries concerned," Ban said after a joint press conference with the President of the International Committee of the Red Cross Peter Maurer in an unprecedented joint call in wake of the world's humanitarian crises here in Geneva.The Islamic State on Saturday claimed responsibility for the crash of a Russian plane earlier the day in Egypt's Sinai, which killed more than 200 people on board.The Sinai-based group "Sinai State" that had announced loyalty to the IS said in a statement posted on Twitter that its militants managed to target the Russian plane and killed all its passengers, in revenge for Russia's military operations in Syria.