HARARE, Zimbabwe (AP) _ The head of Zimbabwe's main opposition party was detained for four hours and two of his aides remained in police custody today after clashes between rival party supporters, the opposition group said.

Morgan Tsvangirai, leader of the Movement for Democratic Change, was stopped at a police roadblock after a campaign rally in Chiredzi, 300 miles south of Harare, party spokesman David Coltart said.

There were clashes outside a gas station in the town and one ruling party official was cut on the head, he said.

Tsvangirai was not there but was on the way to Harare when he was detained, Coltart said.

An opposition security adviser, former police officer John Nkutazo, and party administrator Dennis Murira, both of whom were following Tsvangirai's car, were arrested and taken to a police station at Triangle, a nearby sugar plantation, Coltart said.

They were not informed of any charge, he said.

No ruling party supporters were arrested after the clashes.

Police were not immediately available for comment.

Tsvangirai's party is seen as the biggest threat to President Robert Mugabe's hold on power since he led the nation to independence from Britain in 1980.

Since the party led the defeat of Mugabe's ruling party in a referendum on a revised constitution in February, violent mobs and ruling party militants have staked claims to land on more than 1,000 farms, many of them owned by white opposition supporters.

The political violence has claimed at least 17 lives. On Friday, farmers' leaders reported worsening intimidation against workers on white-owned farms accused of supporting the opposition party.

The worst economic crisis since independence, soaring inflation and unemployment and gas shortages have fueled support for the main labor-backed opposition group ahead of elections expected to be called next month.