At least 13 people were killed and another 25 were injured when Somali militants clashed with government forces in Mogadishu, an official said.

Somali army Col. Hassan Musse told Bloomberg News that al-Shabaab militants attacked Somali and African Union forces late Sunday on a main thoroughfare.

"The number of casualties varies because some were collected by their close relatives before our arrival but our staff has so far picked up 13 corpses and 25 wounded," he told the news agency.

Al-Shabaab representatives said they killed at least eight Ugandan soldiers in the raid.

Somalia hasn't had a functioning government since 1991 and is one of the most corrupt nations in the world. The transitional government controls only a small fraction of the war-torn country.

Somali President Sharif Sheikh Ahmed, nevertheless, called on pro-government forces to stand strong against the looming security threat.

"I call on all parts of the national army and their military commanders to occupy the front line of battle zones, flying our national flag in order to uproot al-Shabaab and their al-Qaida allies from the country as soon as possible," he was quoted as saying.