Recent challenger for Mugabe's presidency brands result 'coup by ballot', hinting that a popular uprising may be way forward

Morgan Tsvangirai, striving to overturn his defeat in Zimbabwe's presidential election, has given his biggest hint yet that a popular uprising is the only option left for resisting the regime of the president, Robert Mugabe.

According to the national election commission, Mugabe won 61% of the vote compared with Tsvangirai's 34%. The result was branded a "coup by ballot" by the opposition leader. But on Sunday the polls result was endorsed by South Africa, leaving Tsvangirai isolated and fast running out of alternatives.

"Revolutions are not called by leaders," Tsvangirai, head of the Movement for Democratic Change (MDC) told South Africa's eNews Channel Africa. "Revolutions are something that is inside, and if you've got something inside and it drives you to do something, then nothing can stop you. In this case, there's no strategy for the leadership of the MDC. We've told people, there's been a subversion in 2002, there's been a subversion in 2008, there's a subversion now. The power is in your hands. It cannot be a revolution by the leadership."

The MDC has consistently renounced violence and resisted calls to organise street protests against what it regards a stolen election. But last week Roy Bennett, the party's treasurer-general who is exiled in South Africa, called for a campaign of passive resistance to bring the country to a standstill.

Other officials floated the idea of a mass prayer meeting. But Harare, the capital, was calm on Sunday with many residents going to church as usual.

In his eNCA interview, Tsvangirai, 61, added: "Remember that this democratic struggle has been a struggle with so many frustrating episodes. For me, I think this is the most frustrating event of my life because I thought that like everyone else in the world, president Mugabe, Zanu-PF, would respect Zimbabweans. But I have seen that they have no respect for Zimbabweans. They have respect for themselves and their power."

Mugabe's Zanu-PF party also won three-quarters of the seats in parliament, leaving the MDC at one of the lowest ebbs in its 14-year history. Party members have complained about the printing of surplus ballot papers, irregularities in the voters' roll, traditional leaders "frogmarching" villagers to the polls, people feigning illiteracy to be "assisted", voters being bussed to faraway constituencies, and the malign influence of the military.

"It's not the reflection of the will of the people," said Tsvangirai, who was prime minister under Africa's oldest leader in an uneasy coalition government. "I don't think that even those in Africa that have committed acts of ballot rigging have done it such a brazen manner."

He spoke as a division between Africa and the west opened up over the integrity of last week's polls. The UK, US and Australia lined up behind Tsvangirai while the African Union and South Africa took 89-year-old Mugabe's side in what critics saw as a sacrifice of principle for the sake of regional stability.

Following deep reservations expressed by William Hague and John Kerry, Australia's government called for a re-run of the election, warning that it would not lift sanctions unless free and fair polls were held.

The foreign minister, Bob Carr, said: "Given our doubts about the results, Australia calls for a re-run of the elections based on a verified and agreed voters roll."

But the South African president, Jacob Zuma, who has led the Zimbabwe mediation process in recent years, offered "profound congratulations" to Mugabe.

His office said Zuma "urges all political parties in Zimbabwe to accept the outcome of the elections as election observers reported it to be an expression of the will of the people".

The verdict comes as a hammer blow to the MDC which has previously praised Zuma for taking a tougher line against Mugabe than his predecessor, Thabo Mbeki. In effect it destroys Tsvangirai's last hope of appealing to the southern African regional bloc to intervene and nullify the election. It also leaves Britain and its western allies marginalised.

South Africa's main opposition party, the Democratic Alliance, gave a scathing response. The shadow foreign minister, Ian Davidson, said: "By congratulating Robert Mugabe on his stolen election president Zuma has failed Zimbabwe, failed Zimbabweans and failed the Southern African Development Community by not providing the leadership that the region desperately required.

"President Zuma's congratulations are not only extremely premature, given the very serious irregularities that have been noted in the elections, but shamefully legitimise undemocratic practices during elections, and send a message that significant irregularities will be tolerated by his administration."

In Zimbabwe, independent domestic monitors said the polls were "seriously compromised" by registration problems that may have disenfranchised up to a million people.

The anti-corruption watchdog Global Witness has alleged that state diamond revenues were spent on securing Mugabe's re-election.

Zanu-PF has rejected all vote-rigging allegations but on Saturday one of the nine members of the election commission resigned over the way it was conducted.

The commissioner, Mkhululi Nyathi, said in his resignation letter: "While throughout the whole process I retained some measure of hope that the integrity of the whole process could be salvaged along the way, this was not to be."