JERUSALEM, April 18 (Reuters) - An explosion aboard a bus in Jerusalem caused around 20 casualties on Monday, Israeli media said, and police said initial indications were that it was a militant attack.

Television images showed smoke billowing from a burned-out bus on Derech Hebron, in southwest Jerusalem. It was not immediately clear if the casualties were dead or wounded. (Writing by Dan Williams; Editing by Alison Williams)

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