Islamist rebels said they shot dead a Somali lawmaker in Mogadishu on Saturday and threatened to kill every legislator in the country.
"How many times had we warned Somalis against joining the infidel government?" Sheikh Abdiasis Abu Musab, spokesperson for military operations for the Islamist militant group al Shabaab, told Reuters late on Saturday.
"Let it be a good lesson for the rest."
Mohamud's election was hailed by his supporters and Western powers as a vote for change after more than two decades of violence. The militants were swift to brand the political newcomer a "traitor" who headed a government serving only Western interests.
Mohamud was the target of a failed suicide bombing just two days into his new job.
"We killed legislator Mustaf ... and we will kill all Somali MPs and officials one by one," Musab said.
The appointment of a new, slimmed-down Parliament and the first presidential vote came as African troops prepared an assault on al-Shabaab's last stronghold in the south of the country.
The African Union Amisom force said, however, there were signs of deepening internal rifts within al-Shabaab. More than 200 rebels defected near the town of Jowhar, about 80km from the capital, on Saturday, Amisom said.
There was no immediate reaction from al-Shabaab.
While the loss of Kismayu and its port would weaken the rebels' morale and deprive them of a key revenue source, it would unlikely deliver a knockout blow to the insurgency.
Diplomats expect al-Shabaab to retreat to the hinterlands, as they have done before, and resort increasingly to the suicide bombings and targeted assassinations that have marked Mohamud's first two weeks in power. - Reuters