KAMPALA, Sept 3 (Reuters) - Twelve Ugandan soldiers who served as African Union peacekeepers were killed when militants attacked their base in Somalia this week, a Ugandan military spokesman said on Thursday.

The statement suggests a lower death toll than the 70 claimed by al Shabaab, which carried out Tuesday's attack, although spokesman Paddy Ankunda said he could not confirm if peacekeepers of other nationalities had been killed.

The AU peacekeeping mission, known as AMISOM, has not yet released casualty figures for Tuesday's attack, which came roughly a year after al Shabaab leader Ahmed Abdi Godane was killed in a U.S. air strike.

"We won't relent in our efforts to pacify Somalia, it's a mission we must accomplish no matter what," Ankunda told Reuters after announcing that the bodies of the 12 Ugandan soldiers would be flown home this week.

Akunda said the delay in announcing the death toll was due to protocol requiring next of kin to be informed first.

Somalia-focused diplomatic sources had initially said the toll was expected to be "very large" lending some credence to the figure claimed by al Shabaab.

But one source said on Thursday that fewer people may have been killed in the attack than previously feared, although the number would only be clear when AMISOM announced it.

Al Shabaab often exaggerates the success of its attacks, while officials play down losses.

The attack on Janale base, about 90 km (56 miles) south from capital Mogadishu, was the latest of its frequent assaults on AMISOM's bases or convoys by the Islamist group which wants to topple Somalia's Western-backed government. (Reporting by Elias Biryabarema; Writing by Drazen Jorgic; Editing by Edmund Blair and Catherine Evans)