Witnesses in the southern Somali port city of Kismayo say an explosion has killed two people and wounded at least 16 others.

The blast ripped through a public park where security officials and regional leaders gathered for a ceremony Sunday.  A police chief from southern Somalia was among the wounded.

Witnesses say police fired into the crowd after the blast.

Mogadishu has been plagued by sporadic violence since the interim Somali government, backed by Ethiopian troops, drove Islamists out of the capital in December. 

Kismayo was the last major city held by the radical Islamist movement.

On Saturday, assailants fired grenades and mortar shells in the capital, Mogadishu.  Five people were killed, including three children.

Islamist leaders have vowed to mount an Iraq-style insurgency against the government.  Some violence also is believed to stem from rivalries among clans and warlords.

The African Union has managed to raise a peacekeeping force of 4,000 troops to help stabilize the nation.

The A.U. says 8,000 troops are necessary to replace Ethiopian soldiers who have begun withdrawing. 

Some information for this report was provided by AFP, AP and Reuters.