Hundreds of protesters have burned flags and threatened to attack African troops set to be deployed to Somalia's capital, Mogadishu.
There have been several protests against the peacekeepers
The 800 demonstrators, in the north of Mogadishu, a stronghold of the ousted Islamists, set fire to Ethiopian, Ugandan and US flags.
Meanwhile, diplomats from Europe, Africa and the US have called for the peacekeepers to be deployed urgently.
The African Union is struggling to raise 8,000 troops for Somalia.
The force is intended to replace Ethiopian troops who helped government forces oust the Union of Islamic Courts, but who have started to withdraw from Somalia.
'Ready to fight'
Dozens of people have been killed in a series of attacks in Mogadishu since the UIC was ousted from the city they had controlled for six months.
It is not clear who is behind the attacks but some Islamists have threatened to wage a guerrilla war.
"We are against any kind of foreign military intervention and we are ready to fight them," protest organiser Mohammed Nur told the AFP news agency.
But the International Contact Group for Somalia, which includes countries from Africa, Europe and America, has reiterated the need for peacekeepers at a meeting in Tanzania.
They also called for reconciliation talks that would include moderate Islamists.
President Abdullahi Yusuf has rejected such calls.
The AU has only raised half of the required force to be deployed to Somalia.
Uganda, Nigeria, Ghana and Burundi are the only countries that have pledged to send their soldiers.
Somalia has not had an effective national government for 16 years.