The African Union has declared Zimbabwe's presidential election as "free and credible," but wants more information about reported irregularities.
Olusegun Obasanjo, who led the AU's election observer mission, said Friday there were "incidences that could have been avoided and even tended to have breached the law."
Obasanjo said his team observed large numbers of voters who were turned away from polling stations. But he said he does not believe this was widespread enough to affect overall outcome of the vote.
The party of longtime President Robert Mugabe has claimed victory in the Wednesday election, although final election results have not been released.
His opponent, Prime Minister Morgan Tsvangirai, on Thursday called the vote a "sham election that does not reflect the will of the people."
"It is our view that this election is null and void, does not meet AU, SADC, international standards for credible, legitimate, free and fair elections," Tsvangirai told reporters." For those MDC-T MPs [members of parliament] who are said to have won, this is not the moment to celebrate. This is the moment to be sad."
In Washington, the U.S. State Department said early reports showed a peaceful election environment. But spokeswoman Marie Harf said Thursday it was too early to say if the polls had been fair.
"Now the critical test is whether voting tabulation is conducted in a credible and transparent manner, and whether the outcome truly reflects the will of the people of Zimbabwe," she noted.
Zimbabwe's Electoral Commission called the election "free and fair." The commission has yet to release any results, saying Thursday that ballots are still being counted. Full results are expected by Monday.
The Zimbabwe Election Support Network, which had thousands of vote monitors throughout the country, also raised concerns about the election. Deputy chairperson Irene Petras said Thursday the process was compromised, with a large number of people being blocked from casting ballots.
"Generally the environment was relatively calm and peaceful," she remarked. "Based on the empirical reports from our observers, regardless of the outcome, the credibility of the 2013 harmonized elections is seriously compromised by a systematic effort to disenfranchise urban voters, up to a million voters."
Police in Zimbabwe have warned they will arrest anyone who gives unofficial vote tallies.
Also, authorities have deployed riot police near the headquarters of Tsvangirai's Movement for Democratic Change (MDC) party.
In the past, vote monitoring groups in Zimbabwe have issued independent tallies based on results from polling stations after preliminary counts. But late Wednesday, police vowed a crackdown that extends to the online publication of any results issued before the country's electoral commission does so.
Mugabe, 89, and Tsvangirai, 61, were the main contestants in the five-candidate race that is expected to end a fragile power-sharing government the two principals were forced to put together in 2009.
It is Tsvangirai's third attempt to unseat Mugabe, who led the country to independence in 1980.
The 2009 power sharing deal, spawned by Tsvangirai's accusations of fraud, ended a round of post-election unrest that left 200 of the challenger's supporters dead.