Morgan Tsvangirai, Zimbabwe's opposition party leader, was released Wednesday after being detained by police for more than eight hours while campaigning for the upcoming presidential run-off vote, media agencies quoted his lawyer and party officials as saying.

The Movement for Democratic Change leader was detained after his convoy was stopped at a roadblock outside the city of Bulawayo around 10 a.m. local time, party officials said.

Tsvangirai and about 14 MDC officials were held at a police station in Lupane, north of Bulawayo, according to the officials. No charges have been filed.

"They've just been released without charge," Reuters quoted Tsvangirai's lawyer Job Sibanda as saying. "The police were saying he addressed an unsanctioned meeting.… They were held for 8 hours before their release."

Tsvangirai, 56, won the March 29 first round of voting against longtime President Robert Mugabe but failed to secure the simple majority necessary to avoid a run-off, according to official results. Mugabe, 84, has been in power since Zimbabwe became independent from Britain in 1980.

The second round of voting is set to take place on June 27.

Human rights groups have said opposition supporters have been beaten and killed by ruling party thugs to guarantee victory for Mugabe.

The MDC leader returned to Zimbabwe in late May after leaving the country for six weeks due to alleged death threats. His party accused the military of plotting to assassinate the presidential candidate.

Tsvangirai has survived at least three assassination attempts. Last year, he was severely beaten by police at a prayer rally.

With files from the Associated Press