A clash between government forces and Islamist rebels left at least 10 people dead and 40 wounded in Somalia's capital Sunday, ambulance crews reported.

Heavy shelling in Mogadishu followed an attempt by government troops to ambush fighters from the al-Shabaab movement, which is trying to topple Somalia's shaky national government, witnesses reported.

Al-Shabaab has ties to al Qaeda and is considered a terrorist organization by the United States. Its war against Somalia's U.N.-backed transitional government has escalated a long-running humanitarian crisis in the Horn of Africa nation, which has not had an effective central government since 1991.