"In practical terms, you have two ministers, one appointed by Zanu-PF, one by MDC," he said.
'Shocked and saddened'
Control of the home affairs ministry has been one of the main sticking points in implementing the power-sharing deal and Tsvangirai said co-managing the ministry with Zanu-PF was unworkable, citing the party's contempt for the MDC.
Tsvangirai said he was "shocked and saddened" by the regional summit's decision.
"The MDC is shocked and saddened that Sadc summit has failed to tackle these key issues ... a great opportunity has been missed by Sadc to bring an end to the Zimbabwean crisis," he said at a news conference after more than 12 hours of talks at the summit.
He added that the Sadc lacked the "courage and decency to look Robert Mugabe in the eyes" and tell him his position was wrong.
Salamao acknowledged that Tsvangirai did not agree with the resolution that responsibility for the home affairs ministry be shared.
"But Sadc was asked to rule and Sadc took a decision and that's the position of Sadc. Now it's up to the parties to implement," he said.
Al Jazeera's Zeina Awad, reporting from Johannesburg where the meeting took place, said Mugabe appeared happy with the outcome and his Zanu-PF party said it was a good basis to move forward.
Tsvangirai beat Mugabe in a presidential election in March but did not garner enough votes to prevent a runoff.
|Robert Mugabe accepted the proposal to share the home affairs ministry with the MDC [EPA]
He subsequently pulled out of the second round, complaining of violence towards his supporters, leaving Mugabe to be declared president.
The two men eventually agreed to form a unity government after months of deadlock and violence which Amnesty International says has left 180 dead and 9,000 injured since March.
But the sides failed to agree on a cabinet and Mugabe proposed a cabinet that would lock Tsvangirai's MDC out of critical posts.
Tsvangirai told the summit he wanted parity in the distribution of ministries, saying that if Mugabe held the defence ministry, the MDC should have control over home affairs, according to his prepared statement.
Opening the talks, Kgalema Motlanthe, South Africa's new president, urged both sides "to show political maturity" in finding a compromise.
"The historic power-sharing agreement remains the only vehicle to help extricate Zimbabwe from her socio-economic challenges," Motlanthe said.