Reports this week that Zimbabwean political party negotiators were close to an agreement in a follow-up round of power-sharing negotiations proved overly optimistic as the fourth day of mediated discussions ended Friday without yielding a compromise agreement by President Robert Mugabe and prime minister-designate Morgan Tsvangirai.

Tsvangirai told reporters late Friday that the negotiations mediated by former South African president Thabo Mbeki had failed to break a deadlock between his Movement for Democratic Change and President Mugabe's long-ruling ZANU-PF party. He said the matter will be put before the committee on politics of the Southern African Development Community.

Tsvangirai added that the talks had been confined to the issue of the equitable distribution of ministerial portfolios, but that negotiators would eventually have to revisit certain language in the Sept. 15 agreement and resolve the question of provincial governor appointments.

Hopes of a resolution were raised earlier Friday after Mr. Mugabe expressed optimism on his arrival at the Rainbow Towers Hotel talks venue declaring, "It is a day for deals.” Tsvangirai was less effusive, telling reporters, "We all have to have hope, don't we?"

Differences over which cabinet portfolios, including in particular Finance and Home Affairs, are to be allocated to Mr. Mugabe's ZANU-PF and the MDC formations headed by Tsvangirai and Arthur Mutambara, have prevented the formation of a national unity government.

The country meanwhile continues to slide into economic and social disarray with hyperinflation running at an official 235 million percent and millions in need of food assistance.

Correspondent Thomas Chiripasi of VOA's Studio 7 for Zimbabwe told reporter Blessing Zulu that the matter seemed increasingly likely to be referred to the Southern African Development Community and the African Union, guarantors of the Sept. 15 power-sharing compact.

The U.S. government stepped up pressure on Mr. Mugabe to make concessions and keep the power-sharing agreement alive. Assistant Secretary of State for African Affairs Jendayi Frazer warned from Tokyo that new financial and travel sanctions targeting President Mugabe, his associates and related companies could be imposed if power-sharing fails.

Some observers said the real cause of the deadlock was apprehension among senior members of the country's security establishment that a government of national unity might prosecute them for alleged crimes of political violence committed during the 2008 election period.

Political violence broke out after the combined MDC broke ZANU-PF's grip on the legislature and Tsvangirai achieved a plurality over Mr. Mugabe in the March presidential ballot. ZANU-PF is alleged to have orchestrated the violence to punish voters who shifted their loyalties and to intimidate the population ahead of a June presidential run-off election. Tsvangirai withdrew from the run-off over mounting violence and Mr. Mugabe claimed victory.

Political sources say a motion by MDC house members calling for an investigation by a select committee could derail the power-sharing process. ZANU-PF insiders say the Joint Operations Command comprising the heads of the national security services has brought pressure on President Mugabe to given them assurances they will not be prosecuted.

ZANU-PF Chief Parliamentary Whip Joram Gumbo, who has approached the MDC speaker, Lovemore Moyo, urging that the motion for an investigation be withdrawn, told reporter  Blessing Zulu that motion is contrary to the spirit of power-sharing.

Chief Whip Innocent Gonese of the MDC formation led by Tsvangirai responded that it is simply a matter of establishing the truth so that such a national trauma will not recur.

More reports from VOA's Studio 7 for Zimbabwe...