Prime Minister Morgan Tsvangirai told party supporters that Roy Bennett "must be treated fairly and the malicious prosecution must stop."

Tsvangirai had nominated Bennett to be deputy agriculture minister in his troubled coalition government with President Robert Mugabe's ZANU-PF party. Bennett, 52, also is treasurer of Tsvangirai's Movement for Democratic Change.

"ZANU-PF must show to the world that they are serious and are committed to democracy," Tsvangirai told a rally on the outskirts of Harare, the Zimbabwean capital.

Bennett's case dates to 2006, when a weapons dealer was arrested and initially accused of plotting to assassinate longtime President Robert Mugabe.

The dealer, who was ultimately convicted of weapons possession, told reporters that police had tortured and forced him to make a false confession implicating several people from both Mugabe's party and Tsvangirai's party, including Bennett, in the alleged plot.

No one else has been tried in connection with the dealer's alleged confession. Bennett had not been linked to the case until his arrest in February, when he was initially charged with treason.

Tsvangirai withdrew from the coalition last month, citing Bennett's case as well as accusations of human rights abuses by ZANU-PF militants and security forces loyal to Mugabe. Tsvangirai also accused Mugabe of treating him like a subordinate and not a coalition partner.

After a three-week boycott, Tsvangirai announced Thursday he was returning to the coalition, saying he was persuaded to relent following South Africa's pledge to monitor the power-sharing deal.

"So tomorrow we are starting to work with Mugabe again in government," Tsvangirai said Sunday.

South Africa and other neighboring countries pushed Mugabe and Tsvangirai to form their unity government in February following a series of inconclusive elections marred by violence blamed on Mugabe's supporters.

Tsvangirai said that, a regional summit last week, South African President Jacob Zuma had promised to intervene diplomatically "to clear all the outstanding issues" if Zimbabwe's government could not resolve its feuding within the next 15 days.