After elections on March 29, Mugabe's Zanu-PF party lost its majority in parliament for the first time in 28 years and Tsvangirai won the presidential election, but without the overall majority required for an outright win.
A delay in the release of election results triggered a wave of violence across the country, particularly in rural areas.
The MDC says that since March more than 50 people have been killed by elements of Zanu-PF in election-related attacks.
Zimbabwe has ordered aid groups Save the Children UK, CARE International and ADRA to stop work in the country immediately, the director of a national NGO association said on Wednesday.
The government has sent letters to the groups issuing the orders, Cephas Zinhumwe, chief executive of the National Association of Non-Governmental Organisations (NANGO), said.
Zinhumwe said he had met with the three organisations he named as being sent the letters.
NANGO had earlier issued a statement saying several unnamed organisations had been ordered to cease operations over accusations that they campaigned for the opposition ahead of an upcoming presidential run-off election.
The association said it was "deeply disturbed by the fact that several NGOs, including those in the humanitarian sector, have been banned from delivering humanitarian assistance and other crucial services they are registered to deliver."