JOHANNESBURG (Sapa-dpa) - Zimbabwe's opposition Movement for Democratic Change (MDC) Sunday said it was committed to reaching an agreement with President Robert Mugabe on the formation of a government of national unity, but warned him against convening parliament before a deal comes through.

"Failure is not an option in this dialogue," MDC secretary-general Tendai Biti told a press conference at the close of a two-day Southern African Development Community (SADC)summit in Johannesburg.

Biti said he was confident the dialogue would be concluded "very soon" but, in an apparent reference to Mugabe, added that one of the parties to the talks had "no business negotiating unless they are prepared to compromise."

Biti also warned Mugabe against convening parliament, a move the MDC opposed.

A last-minute meeting of the SADC organ on politics, defence and security said: "While negotiations (on a government of national unity) are continuing, it may be necessary to convene parliament to give effect to the will of the people as expressed in the parliamentary elections held on 29 March 2008."

Biti responded: "We hope that no one would do anything to breach the memorandum of understanding on the talks."

The July 21 memorandum, which set down rules for the tripartite talks, orders that the parties not convene parliament or form a new government "save by consensus."

A senior MDC official said the party viewed the SADC statement as an attempt to pressure it into agreeing to a deal, but vowed it would not work.

"We don't have consensus to reconvene parliament. How do you reconvene parliament with an illegitimate government?" the official told Deutsche Presse-Agentur dpa.

Mugabe's Zanu-PF party has been calling for parliament to be reconvened since opposition leader Morgan Tsvangirai backed away from a power-sharing agreement earlier this week that would have seen Mugabe retain some executive powers.

Tsvangirai's MDC faction took more votes than Zanu-PF in the March elections but Arthur Mutambara, the leader of a splinter faction of the MDC that holds the balance of power between the two groups in parliament and is a party to the talks, has said he would consider working with either.

Biti said the sticking point in the talks - the division of powers between Mugabe and Tsvangirai, if Tsvangirai is made prime minister as proposed under a draft deal - was a point "of principle."

The MDC official said there had been no progress towards a deal at the summit and that the party had "stuck by its guns."

Tsvangirai, who took the most votes for president in the March election, is pushing for full control of government while Mugabe is looking to share authority.

Mbeki, who had been talking of the possibility of a deal over the weekend, reiterated his hopes for a "speedy conclusion to the negotiations so that it becomes possible to address the enormous challenges that face the people of Zimbabwe."

Mugabe's attendance as head of state at the summit was controversial.

Botswana's President Ian Khama, who refuses to recognize Mugabe's victory in a one-man June presidential election widely derided as a sham, boycotted the summit.

Zambia, whose ailing President Levy Mwanawasa has been openly critical of Mugabe, said the election had "left a serious blot on the culture of democracy in our sub-region."

Zimbabweans are hoping a negotiated settlement will rescue thecountry from the brink of economic collapse.

Mugabe's populist policies over the past decade are blamed for inflation of several million per cent and widespread hunger.

Western powers such as Britain and the United States have vowed to plough money into the country's reconstruction if Tsvangirai and the MDC head the unity government and Mugabe takes a back seat.