* African Union says not deterred by latest attack

* Number of casualties unclear (Adds details of end of attack, killing of official in Kismayu)

By Feisal Omar and Abdi Sheikh

MOGADISHU, June 26 (Reuters) - Al Shabaab militants detonated a car bomb and battled African Union troops at a peacekeepers' base south of Mogadishu on Friday, the latest in a series of attacks in Somalia, military officials and a rebel spokesman said.

In another attack, al Shabaab killed a senior military commander in the port city of Kismayu, a Somali official said.

The attack on the camp in Leego came as residents gathered for morning prayers, the latest in a series of assaults since the Islamic holy month of Ramadan began a week ago. Such attacks during Ramadan are a hallmark of the Islamist militants fighting to overthrow the Western-backed Mogadishu government

The Leego attack started with a car bomb ramming into the base, going past soldiers who tried to stop it by firing at it, Somali Major Nur Olow said.

Fighting had ended by 9 a.m. local time (0600 GMT), and the town was now calm, said Abdikadir Mohamed Sidi, governor of the Lower Shabelle region where Leego is situated.

"Leego town is neither in the hands of AMISOM" - the African Union Mission in Somalia - "nor al Shabaab," Sidi said. "There are many casualties from both sides. We do not know the exact figure of casualties at the moment."

Al Shabaab had also kidnapped several senior local government officials working for the government in Leego, as well as a Somali translator working for Burundi, Sisi said.

Sheikh Abdiasis Abu Musab, al Shabaab's spokesman for military operations, said it had killed 50 Burundian soldiers and lost six of its own fighters. The group often gives higher death tolls than officials do.

In a separate attack in Kismayu on Friday, al Shabaab said it killed a senior military commander.

"Mursal Geddi died after a roadside bomb hit his car. We believe al Shabaab was behind his killing," Isa Aden, a military official, told Reuters from Kismayu.

Last week, al Shabaab - which aims to topple Somalia's government and impose its own strict version of Islamic law - attacked an AU convoy with Ethiopian soldiers along the same route.

It also staged two attacks in Mogadishu in the past week. On Sunday, militants stormed a national intelligence agency training site and on Wednesday it targeted military instructors from the United Arab Emirates with a car bomb.

No Emirates citizens were killed but at least three Somali soldiers died in that attack.

An AMISOM and Somali army offensive last year pushed al Shabaab out of its major strongholds. But the group still controls some rural areas and stages regular attacks in Somalia and neighbouring Kenya.

Maman Sidikou, the representative of the chairperson of the African Union Commission for Somalia and head of AMISOM, said the Leego attack would not deter the group's campaign against al Shabaab.

"This attack will not dampen our resolve to continue to support the Somali government and people until they are free from terrorism," he said in a statement. (Additonal reporting by George Obulutsa in Nairobi; Writing by Edith Honan; and George Obulutsa Editing by Larry King)