HARARE, Zimbabwe — On the eve of elections in Zimbabwe, longtime President Robert Mugabe denied on Tuesday that his supporters have engaged in vote-rigging despite widespread allegations of irregularities in the run-up to the polls. He also said he would step down if he loses the elections after 33 years at the helm of a once prosperous nation whose economy is now in dire shape.

Western governments have condemned previous elections won by Mugabe, alleging the vote was swayed by political violence, intimidation and ballot rigging. While this campaign has so far been far less violent than past elections, there are numerous signs that the electoral process has been vulnerable to manipulation, raising prospects of more political uncertainty ahead.

"We have done no cheating, never, ever," Mugabe, 89, told a news conference in Harare on the eve of polling that begins at 7 a.m. (0500 GMT.)

He brushed aside allegations that loyalist commanders in the police and military will not accept a poll victory by Prime Minister Morgan Tsvangirai, 61, the former opposition leader, and allow him to succeed as the nation's new president. In previous campaign appearances, however, Mugabe has leveled harsh attacks on Tsvangirai.

Mugabe described campaigning as peaceful except for "a few incidents here and there" and said any unrest surrounding contested results will be stopped.

But independent election monitors say the state election commission, dominated by Mugabe's sympathizers, is poorly prepared to hold fair polls.

The International Crisis Group has said conditions for a free vote were not in place.

"Confidence in the process and institutions is low. The voters roll is a shambles, security forces unreformed and the media is grossly imbalanced. The electoral commission is under-funded and lacked time to prepare. Concerns about rigging are pervasive, strongly disputed results are highly likely," said the Brussels-based organization.

It said a return to a protracted political crisis, and possibly extensive violence, was also likely, especially if regional election observers of the Southern African Development Community, or SADC, and the continent-wide African Union failed to identify flaws in the hastily arranged voting process.

The United States voiced its concern over the elections including "the lack of transparency in electoral preparations, by continued partisan behavior by state security institutions and by the technical and logistical issues hampering the administration of a credible and transparent election," said U.S. State Department spokeswoman Jen Psaki on Tuesday. "We are also concerned about long-standing government restrictions on civil society organizations, independent media, political parties and regular citizens that impede their right to operate free of harassment, detention and intimidation."

The Zimbabwe Lawyers for Human Rights said on Tuesday that voters are weighing up their options in the most significant polls since the first elections that swept Mugabe to power in 1980, ending colonial era rule.

Despite complaints of harassment and arrests of rights and civic activists over several months, "we believe a high voter turnout and a determined electorate can still show by their numbers, tenacity and resolve that their vote will be heard and their will respected," the group said.

Mugabe banned observers from the United States, including the Jimmy Carter Center, the European Union and other Western nations. However, observers were permitted from countries deemed friendly, including African countries.

The Zimbabwe Election Support Network, a private group involved in voter education and electoral training programs, is set to deploy 7,000 observers to polling stations nationwide. Another 4,000, including 600 observers from elsewhere in Africa, are also fanning out into voting districts to cover more than 9,000 voting stations.

Mugabe said he expected to see his party as an outright winner, thereby avoiding mediation to form another power-sharing coalition similar to the deal forged by regional leaders after the last disputed and violent polls in 2008.

Tsvangirai has also predicted winning the poll, which he says will usher in change. He has criticized Mugabe's party for doing little except emphasizing its liberation credentials going back four decades.