Freeman Mbowe, who heads the CHADEMA party, and scores of supporters staged a demonstration Monday in the country's northern town of Arusha demanding the release of one of its officials and that Kikwete steps down.

The party accuses the president of using security forces to disrupt its activities.
"He has turned himself in to police," party spokesman Erasto Tumbo told AFP, adding that Mbowe preferred being detained as a sign of protest against the arrests.

Source: Tanzania opposition chief surrenders after demo - Yahoo! News