People hold flowers and candles for victims of the Chernobyl nuclear disaster during a memorial service in Kiev
People hold flowers and candles for victims of the Chernobyl nuclear disaster during a memorial service in Kiev April 26, 2014. Ukraine, Belarus and Russia marked the 28th anniversary of the Chernobyl disaster, the world's worst civil nuclear accident, on Saturday. REUTERS/Valentyn Ogirenko (UKRAINE - Tags: DISASTER ENERGY OBITUARY ANNIVERSARY)
A woman lights a candle before a memorial service for victims of the Chernobyl nuclear disaster in Kiev
A woman lights a candle before a memorial service for victims of the Chernobyl nuclear disaster in Kiev April 26, 2014. Ukraine, Belarus and Russia marked the 28th anniversary of the Chernobyl disaster, the world's worst civil nuclear accident. REUTERS/Valentyn Ogirenko (UKRAINE - Tags: DISASTER ENERGY OBITUARY ANNIVERSARY)
People light candles before a memorial service for victims of the Chernobyl nuclear disaster, in Kiev
People light candles before a memorial service for victims of the Chernobyl nuclear disaster, in Kiev April 26, 2014. Ukraine, Belarus and Russia marked the 28th anniversary of the Chernobyl disaster, the world's worst civil nuclear accident. REUTERS/Valentyn Ogirenko (UKRAINE - Tags: DISASTER ENERGY OBITUARY ANNIVERSARY)
EXCLUSIVE-U.S., EU seen imposing sanctions on Russia on Monday -sources
UKRAINE-CRISIS/SANCTIONS (EXCLUSIVE, UPDATE 1):UPDATE 1-EXCLUSIVE-U.S., EU seen imposing sanctions on Russia on Monday -sources
EXCLUSIVE-U.S., EU to impose sanctions on Russia on Monday -sources
UKRAINE-CRISIS/SANCTIONS (EXCLUSIVE, URGENT):EXCLUSIVE-U.S., EU to impose sanctions on Russia on Monday -sources
A pro-Russian armed man stands guard at a barricade near the state security service building in Slaviansk
A pro-Russian armed man stands guard at a barricade near the state security service building in Slaviansk, April 25, 2014. Armed separatists in the eastern Ukrainian city of Slaviansk seized a bus carrying international observers from the Organization for Security and Cooperation in Europe on Friday, Ukraine's Interior Ministry said. REUTERS/Gleb Garanich (UKRAINE - Tags: POLITICS CIVIL UNREST TPX IMAGES OF THE DAY)
Top Russian general voices concern to U.S. counterpart over Ukraine
UKRAINE-CRISIS/RUSSIA-MILITARY (URGENT):Top Russian general voices concern to U.S. counterpart over Ukraine