Armed members of the Union of Islamic Courts group have increasingly adopted tactics employed by Iraqi fighters since the interim government and its Ethiopian allies forced them out of Mogadishu in December.
They have used roadside bombs and assassinated government officials to fight back, following two rounds of heavy battles that levelled entire neighbourhoods and killed more than 1,300 people in March and April.
Late on Friday, unidentified attackers also threw a grenade and wounded two policemen guarding Mogadishu's seaport.
"The policemen thought the assailants were jokingly throwing stones at them only to realise it was a hand grenade," Abdullahi Abdi, a port worker, said.
The fighters, who also include disgruntled members of the city's dominant Hawiye tribe, have struck government buildings, convoys and have attacked Ugandan peacekeepers patrolling the city under an African Union mandate.
Seyoum Mesfin, the Ethiopian foreign minister, flew out of Mogadishu on Saturday, after arriving the day before to meet with the government about the security situation.
Government sources said he was also discussing the establishment of Ethiopia's embassy to Somalia inside the Villa Baidoa presidential compound.
Abdullahi Yusuf, Somalia's president, is trying to impose central control on the Horn of Africa nation, in anarchy since warlords banded together to oust Mohamed Siad Barre, the former military ruler, in 1991.