Tanzanian officers have shot dead two people during an anti-government protest in Arusha, police say.
Nine people were injured, including three police officers, the city’s police chief Tobias Andengenye said.
The unrest started after the chairman of opposition party Chadema, Freeman Mbowe, was detained, ahead of a rally against government corruption.
Police fired tear gas to disperse the crowd of several thousand people, who demanded Mr Mbowe’s release.
Mr Andengenye said 49 Chadema officials were also arrested in total in the northern city.
“They overstepped the authorisation we gave them,” AFP news agency quotes the police chief as saying.
He said police had given the go ahead for the political meeting, but banned supporters from marching to it.
When this happened Mr Mbowe and several other officials were arrested. The trouble began after the rally.
“They tried to invade police headquarters to free the people who had just been arrested,” Mr Andengenye said.
Three senior opposition leaders, including Mr Mbowe and Chadema’s secretary general and presidential candidate in elections last year, Willibrod Slaa, are to appear in court on Thursday, the party’s spokesman told the BBC.
President Jakaya Kikwete of the CCM was returned to office in November with more than 61% of the vote.
The country boasts East Africa’s second-biggest economy, although more than 50% of Tanzanians still live below the poverty line.