Jewish girls from Ukraine rest at the children center in Kfar Habad near Tel Aviv April 26, 2007. Some 16 Jewish children from Belarus and Ukraine were airlifted to Israel on Wednesday by the Chabad movement, an ultra-Orthodox Jewish sect, and will undergo medical evaluations and treatment. The children will be re-united with their families during their indefinite stay in Israel. Ukraine and Belarus mark on Thursday the 21st anniversary of the world's worst nuclear tragedy when Chernobyl's reactor No. 4 exploded sending radioactive clouds in the air, poisoning vast areas in Ukraine, Belarus and Russia, and contaminating much of Europe.