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BASRA, Iraq, March 25 (Reuters) - Heavy fighting erupted on Tuesday in Iraq's southern city of Basra where Iraqi authorities have clashed with members of the Mehdi Army militia, a Reuters witness said.

An Iraqi military official said Iraqi forces had launched operations to "cleanse" Basra of armed groups.

"Sounds of explosions were heard in different areas of Basra and columns of smoke have been rising from northern districts of the city," the witness said. (Reporting by Aref Mohammed, Writing by Randy Fabi)

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