DONETSK, UKRAINE - APRIL 25: A man holds a Ukrainian flag during a memorial service commemorating the anniversary of the 1986 Chernobyl nuclear accident on April 25, 2014 in Donetsk, Ukraine. The accident, which took place in the northern part of Ukraine, is considered the worst nuclear accident in history. Pro-Russian activists have been occupying government buildings and demanding greater autonomy in at least ten Eastern Ukrainian cities in recent weeks, particularly Slovyansk, prompting the government in Kiev to threaten military action to retake control of the cities. (Photo by Brendan Hoffman/Getty Images)