At least six people were killed and dozens injured in an explosion in northern Syria's Idlib province, officials said Thursday. There was no official statement on the cause of the blast. The UK-based war monitor Syrian Observatory for Human Rights reported that the explosion took place in an ammunition depot. The Syrian Civil Defense, also known as the White Helmets, reported at least six killed in the blast, which took place in the town of Maarat Misrin north of the city of Idlib.