At least 11 people have been killed by a bomb in the market area of the central Somali town of Baidoa.
The governor of the region, Abdifitah Mohamed Gesey, told the BBC that more than 30 other people had been badly injured - mostly women and children.
In February Ethiopian troops seized Baidoa from the Islamist militia al-Shabab.
Witnesses said the bomb exploded shortly after Somali government troops entered the market.
African Union peacekeepers for the first time recently deployed to the town, which is on a strategically important route.
It is one of the biggest attacks in the area since Ethiopian and Somali forces took control.
Baidoa, 250 kilometres (155 miles) north-west of the capital Mogadishu, had been one of the most important al-Shabab bases.
Al-Shabab said it had withdrawn its forces as part of a "tactical retreat" and threatened to start a guerrilla war in response.