(CNN) -- Heavy fighting between Islamist militants and government forces in Somalia's capital has left 18 people dead and dozens wounded, medical officials said Sunday. "The fighting is huge and is marked by heavy exchange of artillery," said Ali Musa, a head of a Mogadishu ambulance service. Of the 36 reported wounded, 11 were hurt when an artillery shell hit their bus near Mogadishu's Bakara Market. The African Union peacekeeping mission in Somalia said the fighting centered around attempts to destroy a network of tunnels and trenches that the jihadist movement Al-Shabaab used to move weapons and fighters around the capital. The dead included two peacekeepers and six rebel leaders that the Ugandan-led mission said were linked to al Qaeda.
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NEW: AMISOM says 5 of 6 slain rebels were non-Somalis
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Ambulance crews report "huge" battles in Mogadishu
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Peacekeepers claim success in battling Islamist militants
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