The secretary general of Zimbabwe's opposition Movement for Democratic Change (MDC) party, Tendai Biti, was detained on his return to Zimbabwe on Thursday, an MDC spokesman said, according to dpa. Biti was picked up at Harare International Airport when he arrived home from a two-month spell in South Africa following disputed elections in Zimbabwe, MDC spokesman Nelson Chamisa said. He was handcuffed by about 10 plainclothes police officers as he left the airport just after midday. Police said Biti, who is also a member of parliament, had been arrested in connection with the announcement of results in the disputed March election. "He has been detained to assist police with investigation regarding accusations," police spokesman Wayne Bvudzijena said. Chamisa said the charges were not immediately clear. But a police crackdown on dissenting voices is seen to be intensifying ahead of a run-off presidential election on June 27. MDC leader Morgan Tsvangirai is challenging President Robert Mugabe in the run-off. "At the moment we are worried about his whereabouts, as the regime is determined to do anything. This is a strategy to disturb us from campaigning? But that will not work," Chamisa said. The MDC and human rights groups accuse Harare of waging a violent intimidation campaign ahead of the run-off and claims Mugabe's ruling Zanu-PF party militia have killed 66 opposition supporters. Zanu-PF, meanwhile, blames for the political violence. Campaigning has taken place in a climate of violence, which, according to the MDC, has claimed the lives of 66 people. Another 200 were missing, 3 000 had had to receive hospital treatment and 25,000 were displaced, it said. The run-off became necessary after the MDC leader defeated Mugabe, in the first ballot on March 29 but failed to win an absolute majority. Mugabe, 84, who has been in power since 1980, has come under fire internationally for the economic collapse of the once-thriving Zimbabwe, which features the world's highest inflation level, acute shortages of food, fuel, electricity, medicines and foreign currency.