Mr Mugabe (right) administered the oath to Mr Tsvangirai in February
South African President Jacob Zuma has asked Zimbabwe's political parties to remove any obstacles to implementing their political agreement.
He was speaking at a two-day meeting of Sadc, the southern African regional organisation, in DR Congo.
Zimbabwean President Robert Mugabe and Movement for Democratic Change leader Morgan Tsvangirai formed the power-sharing cabinet in February.
It was an attempt to end the political crisis after 2008's disputed elections.
Mr Zuma told the Southern African Development Community (Sadc) meeting in Kinshasa that "significant progress" had been made by Zimbabwe's coalition government.
But he added: "We urge all parties to remove any obstacles to the implementation of the agreement."
The BBC's Karen Allen in Kinshasa says Mr Zuma has promised to be more vocal in his criticism, but there is little to suggest a hardening of his stance.
Zimbabwe was one of several items on the agenda at Monday's regional bloc summit, along with climate change and Madagascar.
Sadc has now agreed to hold a separate meeting about Zimbabwe in the coming weeks, possibly in Mozambique.
Our correspondent says the MDC is concerned about the pace of political reform, alleged human rights abuses and appointments of key positions in the legal system and central bank.
She also says Mr Mugabe wants Sadc to campaign for the lifting of economic sanctions against Zimbabwe.