Russia is observing a day of mourning in memory of at least 170 people who died in a plane crash on Tuesday, with religious services, flags at half-mast and television schedules changed to reflect the sombre mood. Most of those killed were Russians. Victims’ relatives have travelled to the disaster zone in Ukraine for a ceremony there today. Among those who died were 45 children. Although lightning was initially blamed for the crash, it remains unclear just why the plane, bound for St Petersburg from the Black Sea resort of Anapa, came down north of Donetsk in Ukraine. Its black box flight recorders will now be studied.