The US has urged the Somali government to talk with moderate Islamists, such as Mr Ahmed - others are believed to already be in Yemen.
But interim President Abdullahi Yusuf says the Islamists are irrelevant after their military defeat in December.
In the capital, Mogadishu, mortars have killed several people.
The attack was the latest in a series of sporadic clashes involving Ethiopian troops, who back the government, and unidentified gunmen in Mogadishu.
The BBC's Mohammed Olad Hassan in the capital says leaflets warning residents not to co-operate with the government have been in circulation in city, and the attacks could be linked to them.