No group claimed responsibility for the attack on Mustafa Haji Maalim late Saturday afternoon, Garowe Online said.
Violence has been mounting in the capital since the Sept. 10 election that brought President Hassan Sheikh Mohamud and a new parliament to power, CNN said. Rights officials say at least 80 people have been killed by political violence since the election.
United Nations special representative Augustine Mahiga issued a statement condemning Maalim's killing.
"These cowardly acts of targeted assassinations and indiscriminate bombings cannot deter the remarkable courage of the Somali people, whose tenacity and determination has overcome formidable obstacles and brought us to where we are now," Mahiga said.
Somalia hasn't had an effective government since 1991 and has been wracked by Muslim sectarian violence since.
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