HARARE, Zimbabwe — Zimbabwean President Robert Mugabe said Friday his party will have to fight hard to win upcoming polls scheduled for the end of this month and ensure its political survival after three decades in power.

Speaking at the launch of his ZANU-PF party's election manifesto, Mugabe said his party will put up a "fight of our lives" to regain waning support in urban areas, strongholds of his main political opponent, Prime Minister Morgan Tsvangirai.

"We have come here to regain what we lost along the way," he said. "This one will be a fight of our lives, we have to battle for survival."

Mugabe's party has been repeatedly accused of political violence, intimidation and vote-rigging in the last three general elections since 2000.

Mugabe, who was forced to form a tenuous coalition government with Tsvangirai by regional leaders after violent and disputed elections in 2008, has ruled the southern African nation since independence from colonial rule in 1980.

Mugabe, 89, will face Tsvangirai, 61, in the national vote he has set for July 31, following a May court ruling ordering him to call for early polls.

Mugabe's partners in the coalition had appealed against the July election, but the Constitutional Court, the nation's highest court, upheld the date on Thursday.

Tsvangirai had asked for a delay of at least 25 days to give time to institute democratic reforms and changes to electoral laws to allow for a free and fair ballot.

Mugabe said calls for a poll delay by the Southern Africa Development Community, a regional, political and economic bloc known as SADC, were interfering with Zimbabwe's court processes.

"Let it be known we joined SADC voluntarily, we can leave and withdraw from SADC," he said.

Addressing tens of thousands of supporters gathered at a soccer field in Highfield, where he held his first victorious rally as he was swept into power in 1980, Mugabe pleaded for support in the polls.

"It was here we started. We don't want to die, we need political life," he said.

Mugabe said his party had learnt from its past mistakes and electoral losses and had become stronger.

"We have come back invigorated to wage a forceful, vigorous and devastating fight. It's a do or die battle," he said.

Tsvangirai claimed he won the last elections in 2008, which he claimed was tainted by political violence and vote-rigging.

Earlier Friday, the former opposition leader in the coalition with Mugabe cancelled a news conference where he was expected to announce an opposition alliance to fight Mugabe's ZANU-PF party in the July poll after the decision by the Constitutional Court to push ahead with elections.

It was expected Tsvangirai had forged an alliance with a breakaway faction of his party to present a united challenge to Mugabe with Welshman Ncube, his chief rival in the democratic political movement, to avoid splitting the vote against Mugabe.

No reason was given for the cancellation, but Ncube has been nominated as a presidential opponent to Mugabe and has resisted previous appeals for him to present a united against Mugabe.

In the 2008 elections, Ncube and another presidential candidate, a former minister in Mugabe's party garnered nearly 10 percent of the vote that stopped an outright Tsvangirai victory and led to a run-off vote for the presidency that Tsvangirai boycotted on allegations of spiraling political violence against his supporters.

Mugabe on Friday called for campaigning without violence that has marred previous polls.

"Let's teach our opponents a lesson ... Let's fight to win," he said.