A special UN military force to protect aid workers deployed for the first time in the war-ravaged Somali capital Sunday, amid a wave of attacks blamed on Al-Qaeda-linked Shebab insurgents.

A special UN military force to protect aid workers deployed for the first time in the war-ravaged Somali capital Sunday, amid a wave of attacks blamed on Al-Qaeda-linked Shebab insurgents.

The 400-strong "defensive" guard force of Ugandan troops, based at the heavily fortified Mogadishu airport, is "mandated to protect UN staff and installations" in the capital.

Despite the government's insistence that it has improved security, the Shebab continue to carry out bombings -- including targeting aid workers -- in their bid to overthrow Somalia's internationally backed but fragile leadership.

Shebab suicide commandos last June blasted their way into a fortified UN base in central Mogadishu, killing 16 people.

"The deployment of the UN Guard Unit is an important step as we continue to expand our operations in support of the Somali people," UN envoy to Somalia Nicholas Kay said at a ceremony Sunday to mark the start of operations.

Ugandan troops are already in Somalia as a key part of the UN-mandated African Union force AMISOM, which is fighting the Shebab.

The insurgents have been driven out of fixed positions in Somalia's major towns by AMISOM troops, but still regularly launch guerrilla raids.