Complex sentence: Officially, the operation was led by Somali government forces, with Kenyan troops providing support, though in reality it was Kenyan troops, with some local Somali militia support, that drove towards Kismayu.
Split into simpler sentences: Officially, the operation was led by Somali government forces, with Kenyan troops providing support. What actually happened was Kenyan troops, with some local Somali militia support, drove towards Kismayu.