Botswana called on Monday for an independent audit of Zimbabwe's disputed vote last week, saying the elections could not be considered acceptably free and fair in the regional southern African community.
The statement from the government in Gaborone contrasted sharply with the unqualified endorsement given by South Africa's president, Jacob Zuma, of the July 31 polls which re-elected veteran Zimbabwean leader Robert Mugabe, 89.
Mugabe's main rival, Morgan Tsvangirai, is challenging the result as a fraud.
Gaborone's assessment also revealed differing views within the 15-nation Southern African Development Community (SADC) whose members include South Africa, Zimbabwe and Botswana. Observers from Botswana were part of a SADC team which monitored the Zimbabwean presidential and parliamentary polls.
The Botswana government said that although the election day itself had been "free of overt intimidation and violence", there was evidence that the electoral process was undermined by a number of irregularities.
"There is no doubt that what has been revealed so far by our observers cannot be considered as an acceptable standard for free and fair elections in SADC," it said.
On Sunday, Zuma had called the Zimbabwean elections "successful" and said the SADC observers had reported the outcome "to be the will of the people".
In contrast, the United States has said it does not believe the vote was credible and the European Union has also expressed concern over alleged serious flaws.