(Adds Baidoa attack)

By Aweys Yusuf and Abdi Sheikh

MOGADISHU, Dec 24 (Reuters) - Burundi deployed a second contingent of 92 peacekeepers to the Somali capital on Monday, to bolster an African Union force struggling to stem violence in the turbulent Horn of Africa nation.

Armed with AK-47s, the soldiers streamed off a Ugandan cargo plane and marched towards an AU base close to Mogadishu airport.

"We are privileged to have Burundian troops deploying here," said AU force commander Major General Levi Karuhanga.

"We appeal to other African countries that pledged peacekeepers to emulate Burundi and deploy their troops to Somalia," he told reporters.

The day before, some 100 Burundi troops landed in the shell-shattered city as part of the first phase of long-delayed support for 1,600 Ugandan troops who arrived in March as the vanguard of a still unrealised 8,000-strong AU mission.

"The Burundian troops have a mission here. They will occupy key positions in the capital," said AU spokesman Paddy Ankunda.

"It could be Bakara (market) or anywhere else to cease hostilities, but we cannot reveal it now for security reasons."

Burundi says the rest of two battalions of 850 soldiers each should be on the ground in the next two weeks.

Without support, the Ugandans have been restricted to guarding Mogadishu's sea and air ports and presidential palace, as well as providing security for top government officials.

However, they have been unable to make much impact on an Islamist-led insurgency against Ethiopian-backed government troops that has uprooted hundreds of thousands of Somalis.

Government troops and insurgents exchanged automatic gunfire and mortar rounds inside Mogadishu's sprawling open air Bakara market early on Monday, forcing hundreds of traders to flee for their lives.

"After the fighting stopped, I came out of my shop and saw three dead soldiers," said storekeeper Mohamed Bashir Hashi.

In the latest violence, assailants threw a grenade at the home of the acting governor of the southern trading town of Baidoa where parliament is based, killing two of his children and a bodyguard, police said.

Persistent insecurity has deterred many nations from sending troops to the country, mired in lawlessness since warlords ousted a dictator in 1991.

As they prepared to board the aircraft in Bujumbura, Burundi peacekeepers said they were ready for one of the world's most dangerous cities.

"I am not frightened at all. We have been well prepared for the peacekeeping mission," said Corporal Gerard Niyonkuru. "We will accomplish our duty of protecting the Somali people."

The United States has helped Burundi, which is still recovering from its own conflict that killed 300,000 people, with logistics. France paid for the airlift of the troops. (Additional reporting by Patrick Nduwimana in Bujumbura and Ahmed Mohamed in Baidoa; Writing by Tim Cocks; Editing by Katie Nguyen and Matthew Jones)

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