At least 12 people have been killed and more than 30 badly injured by a bombing in the central Somali town of Baidoa.The governor of the Bay region, Abdifitah Mohamed Gesey, told the BBC that most of the casualties were women and children.Mr Gesey said the bomb was planted in a small basket and hidden in a busy market in the centre of town.It is the worst attack in Baidoa since Ethiopian troops took control from the Islamist group, al-Shabab, in February.Witnesses said the bomb went off shortly after Somali government troops had arrived in the market."This was a disaster," Adan Hassan, a witness told the AFP news agency. "I saw [the] bodies of at least nine civilians, most of them women. The explosion occurred as people were shopping."A spokesman for al-Shabab's military operations said it was behind for the blast."We targeted the Ethiopian and the Somali troops. About three of them died," Sheikh Abdiasis Abu Musab told the Reuters news agency.In February al-Shabab merged with al-Qaeda, and still controls much of the south of the country.PeacekeepersIt is the second bomb attack in Somalia in less than a week.On Wednesday, eight people were killed in a suicide attack on the national theatre in the capital, Mogadishu.Last week, African Union peacekeepers for the first time deployed to Baidoa, which is on a strategically important route.Baidoa, which is 250km (155 miles) north-west of Mogadishu, had been one of the most important al-Shabab bases.The town had, until they took control three years ago, been the seat of Somalia's transitional government.Al-Shabab said it had withdrawn its forces as part of a "tactical retreat" and threatened to start a guerrilla war in response.