Delegates at the talks said he had been playing a crucial role.
"Maalim Yusuf was a peace-loving elder. We will badly miss him. His death will negatively impact the talks," Abdirahman Ahmed, one of the delegates, told Reuters. "This is a big blow to peace."'Heinous crime'
Haji Abdi Iman, the senior delegate for the Hawiye clan, said: "I don't care who committed this heinous crime but I can say this is a black day for the supporters of peace because he a dedicated negotiator despite his old age."
|"I don't care who committed this heinous crime but I can say this is a black day for the supporters of peace"|
Haji Abdi Iman, senior delegate for the Hawiye clan
Local residents have said that this was the first time a senior clan elder had been killed in living memory.
The capital had experienced a short period of relative calm after a security crackdown coinciding with the July 15 opening of the talks.
Heavy fighting had erupted in Mogadishu's neighbouring Horuwa district hours after Yusuf was killed.
Mortars were fired at police who had taken up positions near a children's hospital.
"Two guards and a man were wounded after mortars landed at the hospital. The insurgents attacked the police from two sides and we were caught in the middle," a security guard said.
"The police responded with heavy artillery - it was really terrifying."