Police banned a rally planned by Zimbabwe’s prime minister on Saturday and some of his supporters were beaten as they approached the event site, plunging the country’s fragile coalition government deeper into crisis.

Prime Minister Morgan Tsvangirai’s party said it would seek a court order allowing their meetings and rallies to be left unhindered.

Authorities had banned Saturday’s prayer and peace vigil, saying it posed a risk of clashes because it coincided with another rally being held nearby for longtime President Robert Mugabe’s party.

Police surrounded the venue west of the city centre where hundreds of Mugabe militants were allowed to gather. Witnesses said Mr. Tsvangirai’s supporters who approached, thinking it was their rally, were chased away and several were assaulted.

Mr. Mugabe, who had been in power since Zimbabwe’s independence in 1980, was forced to join the troubled power— sharing coalition with Mr. Tsvangirai after disputed, violence—ridden elections in 2008. Political violence has again surged since December when Mr. Mugabe called for elections this year to bring an end to the shaky coalition.

Mr. Tsvangirai also has threatened to pull out of the power—sharing deal following the arrest of a top aide, Elton Mangoma, earlier this month on allegations of corruption. Three lawmakers allied with Mr. Tsvangirai also have been arrested on minor charges the party said were trumped up. All deny wrongdoing.

Mugabe hard—liners have even called for Mr. Tsvangirai’s arrest over recent remarks that the nation’s Supreme Court was packed with biased judges loyal to Mr. Mugabe. Mr. Tsvangirai told reporters on Friday his arrest would be “the final nail in this whole delicate and fragile government.”

“If there are those who want to arrest me, I am here ... I don’t want to run away,” he said.

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