HARARE, Zimbabwe — Zimbabwe Prime Minister Morgan Tsvangirai said Friday he is deeply disturbed by chaotic preparations for Zimbabwe's elections on July 31 despite the African Union's approval of the process.

"The credibility of this election is at risk," warned Tsvangirai.

He told a press conference that the state election commission does not appear to be in control of final arrangements, voters' lists still have not been made available to candidates and the registration of eligible voters on those lists was not completed.

"This chaos will lead to inconclusive and contested results," Tsvangirai said.

Tsvangirai, 61, is facing long-time President Robert Mugabe, 89, and three minor candidates for the presidency in the vote set for Wednesday.

Tsvangirai sharply criticized Nkosazana Dlamini-Zuma, chairperson of the African Union, for declaring that he had raised no concerns with her.

Dlamini-Zuma said on a visit to Zimbabwe earlier Friday that AU observers are "satisfied" with arrangements so far.

Tsvangirai said from her past record as South Africa's foreign minister, Dlamini-Zuma had shown bias toward Robert Mugabe and is not seen as an impartial observer.

"We know her background. Why would she want to deny what was said in our meeting?" he said.

Violence and alleged vote rigging have marred Zimbabwe's previous elections since 2000.

After Zimbabwe's last violent and disputed polls in 2008, leaders from neighboring countries forced Mugabe to form a coalition government with Tsvangirai.

Dlamini-Zuma told reporters that AU observers noted that contesting parties have not been given equal access to the state media controlled by Mugabe loyalists. She also noted that there were only a few reports of pre-election violence.

"We hope the peaceful environment will obtain until the end. We plead with everybody to keep the peace and continue stressing that to supporters so that Zimbabweans can express their will," she said.

If the voting results are disputed "it should be challenged legally and not in the streets. People who start violence must be dealt with," Dlamini-Zuma said.

She described both the independent and state media as "highly polarized."

Observers had seen that Mugabe's broadcast monopoly provides live and in-depth coverage of his campaign that is not provided to other candidates, her observer mission said in a statement Friday. They noted that there has been an improvement in political advertising aired by the state broadcaster in the last two weeks, the statement said.

But Tsvangirai said Friday that the state-controlled Zimbabwe Broadcasting Corp. refused to air some of his campaign advertisements saying they are "not suitable for the state media."

In another development, mobile phone companies have been ordered by the state telecommunications body to block bulk text messages that have been successfully used by Tsvangirai's party and independent civic groups to circulate election information, said Kubatana, a group of civic organizations.

Cell phone companies must comply with immediate effect, according to their operating licenses, said Kubatana.

Mugabe's ZANU-PF party has lagged far behind Tsvangirai's Movement for Democratic Change party and civic groups in the use of electronic texting, websites and social media in the election campaign. This new ban on mass cell phone messages is seen as a way that ZANU-PF is trying to stop the effectiveness of Tsvangirai's campaigning through social media. Kubatana said it will immediately appeal the order.