Johannesburg/Harare  - Opposition leader Morgan Tsvangirai was detained by police Wednesday while campaigning in the second round of Zimbabwe's presidential lections, officials of his Movement for Democratic Change (MDC) said.

Tsvangirai, 56, was detained at a police roadblock near the village of Lupane in western Zimbabwe, said his spokesman George Sibotshiwe, who was picked up with him.

MDC vice president Thokozane Kupe and party chairman Lovemore Moyo were also in the group, which was held at the roadblock for a few hours before being taken to a nearby police station, Sibotshiwe told Deutsche Presse-Agentur dpa by telephone from the station in the late afternoon.

Police had not given any indication of why they were holding them, saying only that they were waiting for a senior officer to arrive, Sibotshiwe said.

Tsvangirai returned around 10 days ago to Zimbabwe from more than a month of self-imposed exile in South Africa and Botswana to contest a run-off presidential election against longtime President Robert Mugabe, 84, on June 27.

The MDC leader, who has survived several assassination attempts, said his protracted absence was due to threats to his security.

He has been banned from holding rallies in several towns in the western provinces of Matabeleland, his party's stronghold, for no apparent reason.

Analysts say the MDC is effectively the government-in-waiting after winning a parliamentary majority in elections on March 29, inflicting the first defeat on Mugabe's Zanu-PF party since independence in 1980.

Tsvangirai also won more votes than Mugabe in the presidential ballot but failed to win more than 50 per cent of the vote he needed to be declared outright winner, according to the official count.

Mugabe's wife Grace was quoted as saying last week that even if Tsvangirai wins the run-off he would never enter State House (the president's residence), fuelling suspicion Mugabe could refuse to relinquish power if defeated.

In the past few days a post-election campaign of intimidation against the opposition that has seen at least 50 MDC supporters killed by Mugabe backers has broadened to include MDC leaders, human rights lawyers, journalists and activists.

Arthur Mutambara, leader of a smaller MDC faction, was released on bail Tuesday after being arrested at the weekend over a newspaper article criticizing Mugabe's government and the judiciary.

A prominent human rights lawyer, Andrew Makoni, fled to South Africa in recent days after reportedly receiving death threats.

Several activists with well-known rights group, Women of Zimbabwe Arise, are also in police custody after being arrested for conducting a peaceful march last week.

And three South Africans working for British broadcaster Sky were on Monday sentenced to prison terms of between six and seven-and-a- half months after being found in possession of "illegal broadcasting equipment."

UN Secretary General Ban Ki-moon said Tuesday in Rome said he would send an envoy to Zimbabwe to discuss conditions for a credible run-off election.

But Mugabe, also in Rome for a UN conference on hunger, reportedly snubbed the idea, saying he would not accept "anything that smells of American and British influence." (dpa)