A bomb in the southeastern Turkish city of Diyarbakir Tuesday evening killed seven people and injured 17 others, the local governor's office said. Authorities said the bomb was made from powerful explosives and was set off by a cell phone timer. It was not immediately known who placed it. Diyarbakir Deputy Gov. Ahmet Aydin said children were among the killed and that two of the injured were in serious condition at a local hospital. Local news stations said five of the seven killed were children. The blast apparently took place near an elementary school, a Kurdish news agency reported. Diyarbakir is Turkey's largest Kurdish-majority city, and the explosion comes as Kurdish rebels fighting for autonomy in the region have stepped up their attacks. It is the third suspected bomb attack of the day.