Al Shabaab militants attacked an African Union (AU) base in southern Somalia early on Tuesday
Fighters from the al-Shabab militant Islamist group have overrun an African Union military base in southern Somalia, inflicting heavy casualties, witnesses have told the BBC.
The militants said they have killed 70 AU soldiers at the Janale base, 90km (55 miles) south-east of the capital.
AU forces have insisted they are still in control of the base.
Al-Shabab, part of al-Qaeda, is battling the AU-backed government for control of Somalia.
Residents said the attack started with a suicide car bombing at the base's gate, followed by sustained gunfire which lasted more than an hour.
They told the BBC Somali service that AU forces were seen leaving the base, which is run by the Ugandan troops.
The militants damaged a nearby bridge with a massive bomb to prevent troops from escaping, Col Ahmed Hassan from the Somali army told the Associated Press.
He also said the militants had seized the base.
Captain Bilow Idow, a Somali military officer based in a town near Janale, said the base had been effectively cut off.
"No reinforcement can reach there," Reuters news agency quotes him as saying. "There is much death and damage."
However, the AU mission in Somalia (Amisom) denied it had lost control of the base, without mentioning any casualties.
In June, the group overran another African Union base in Lego, a small town in the Lower Shabelle region in southern Somalia, killing dozens of soldiers and seizing military equipments.
Despite losing most of its key strongholds in south and central Somalia, al-Shabab continues to carry out attacks on the government and African Union troops across the country.
The militants also stage frequent suicide attacks inside the capital, Mogadishu.