Uganda's President Yoweri Museveni says Ugandan soldiers being deployed to Somalia, will not disarm militias.
Uganda's tank battalion will head to Mogadishu via Mombasa
Mr Museveni, who bade farewell to 1,700 troops at a ceremony in Jinja, said they will train the Somali army, help the government, but not impose peace.
An advance team of African Union (AU) troops reportedly arrived in Baidoa in southern Somalia on Thursday.
Some 8,000 AU peacekeepers are to be sent to Somalia to replace Ethiopian troops, who ousted Islamists last year.
Somalia enjoyed a six-month lull in the insecurity that has dogged the country for the last 16 years when the Union of Islamic Courts (UIC) was in power.
But violence has escalated in the past two months.
So far only half of the 8,000-strong force promised have been contributed by AU member states.
Nigeria has said its 850 soldiers will be deployed from the middle of April in three phases. Other countries that have pledged to send troops are Ghana and Burundi.
"We will not go to Somalia to impose peace on the Somalis, because we shouldn't do that and we can't do it," President Museveni said to his troops.
"What we are going to do in Somalia is to empower our Somali brothers to rebuild their state."
But Somalia's government spokesman, Hussein Mahmoud Mohammed, has warned that unless AU troops lead the disarmament process the killings will continue.
An insurgency in the capital, launched by suspected Islamists, appears to be making its mark, with daily attacks - often targeting Ethiopian forces.
More than 10,000 civilians have fled Mogadishu in the past two weeks, the United Nations estimates.
Officials have blamed the rise in violence on the high number of weapons available.
There have been several protests against the deployment of AU forces in Somalia, even though many Somalis are keen to see the departure of Ethiopian forces as quickly as possible.
Islamist insurgents have warned that foreign peacekeepers are not welcome in Somalia.
Uganda officials say a tank battalion leaving Jinja in eastern Uganda is expected to head to Somalia's capital via the Kenya port city of Mombasa while infantry units will be flying to Somalia next week.