Timeline: How the crisis in Ukraine unfolded

A Ukrainian serviceman plays with a child as men believed to be Russian servicemen stand in front of the gates of a Ukrainian military unit in the village of Perevalnoye outside Simferopol, March 4, 2014. President Vladimir Putin has ordered troops that took part in military exercises in central and western Russia to return to base after completing their training, Russian news agencies quoted the Kremlin spokesman as saying on Tuesday. REUTERS/David Mdzinarishvili (UKRAINE - Tags: POLITICS MILITARY)

Key events in Ukraine's political crisis: