Justice Minister Patrick Chinamasa said the ruling party was preparing for a runoff after its tallies showed neither Tsvangirai nor Mugabe won the required absolute majority.
The MDC has rejected both a runoff and ZANU-PF attempts to have at least 14 seats recounted in the parliamentary vote. It says Tsvangirai has won and should immediately end Mugabe's 28-year rule.
SUMMIT
Zambian President Levy Mwanawasa, chair of SADC (Southern African Development Community) called the Saturday summit.
Tsvangirai said he would try to persuade SADC leaders to ask Mugabe to step down.
SADC has been criticised in the past for failing to pressure Mugabe despite the economic collapse in Zimbabwe, now suffering the world's highest inflation, chronic shortages of food and fuel and a near worthless currency.
Mwanawasa's summit call came after Jacob Zuma, powerful leader of South Africa's ruling African National Congress, said the poll results must be released, signalling a more robust reaction to the crisis than President Thabo Mbeki who has insisted on "quiet diplomacy" rather than overt pressure.
The long delay in issuing results has dashed hopes of quick action to turn round a ruined economy that has sent millions of refugees fleeing to neighbouring SADC countries.
The official inflation rate is 100,580 percent but analysts believe the real level is much higher. An independent Zimbabwean newspaper said last week that official figures for February showed inflation at 164,900 percent.
Investors fear that if the Zimbabwean political impasse continues, it could impact on other countries in the region - especially South Africa, whose rand currency has proven vulnerable to political events in its northern neighbour.
Although the rand benefited last week because of optimism that the Mugabe era might be ending, traders said Zimbabwe was not having any effect now, with all eyes on the South African Reserve Bank which raised its key repo rate to 11.5 percent on Thursday because of a surge in inflation.
Traders said negative developments in Zimbabwe were generally discounted by the market but positive news could give the rand some support, although it was not a key driver so far.
