Johannesburg, South Africa (CNN) -- South African President Jacob Zuma is traveling to Zimbabwe on Tuesday to try to save that country's beleaguered unity government.
During his three-day visit, Zuma will assess progress "with regards to the implementation of the power-sharing agreement," according to his office.
Bitter political rivals President Robert Mugabe and opposition party leader Morgan Tsvangirai formed the unity government last February after a disputed presidential election. Tsvangirai became the country's prime minister and Mugabe kept his seat as president.
Zuma took over from his predecessor, Thabo Mbeki, as facilitator of the fragile unity government deal. The pact was signed in September 2008 following spates of post-election violence, but problems have plagued the forced marriage between Mugabe and Tsvangirai.
Tsvangirai's party, the Movement for Democratic Change has accused Mugabe's Zanu-PF of failing to fully implement the deal. And Mugabe has threatened to end the unity government and reclaim power.
Though Mbeki managed to get the two parties to agree to govern jointly, he was accused of being a Mugabe sympathizer.
Before taking office, Zuma showed signs that he might take a tougher stance against the 86-year-old ruler. But critics say Zuma has not and have pointed to recent attempts to get Western leaders to withdraw sanctions against Mugabe and other members of his party.
Tuesday's visit marks Zuma's second official trip to Zimbabwe as president. During his August visit, he urged the country's leaders to implement the unity deal without delay. The situation has since deteriorated.
"I don't know why he is coming. I don't know what he is coming to facilitate," said Mugabe's minister for presidential affairs Didymas Mutasa. "The most important issue is the issue of sanctions. Until sanctions are lifted it is very stupid for any other person to ask us to implement any other matter," he told CNN.
Members of both parties were supposed to share ministerial positions. But at least four ministers from the Movement for Democratic Change, or MDC, have recently been stripped of their powers, the party says.
Mugabe's party is pushing ahead with controversial legislation to transfer 51 percent of foreign-owned companies to black Zimbabweans, at a time when the country desperately needs foreign investment.
The parties also are fighting over the appointments of the attorney general and the reserve bank governor, powerful positions that have gone to Mugabe's party.
"This is not a power-sharing model. They are grabbing power," said MDC spokesman Nelson Chamisa. "Zanu-PF continues to do things with impunity. We need the guarantors of the agreement SADC (the Southern African Development Community) to help us to end this unilateralism."
U.S. President Barack Obama recently extended his country's sanctions against Mugabe and other members of his party. British Prime Minister Gordon Brown refused to reconsider his government's sanctions policy against Mugabe, despite a plea by Zuma.
The South African president's failure to persuade the Western leaders to allow Mugabe and some other party members to resume travel to their countries probably will be discussed during Zuma's trip.