Jendayi Frazer, assistant U.S. Secretary of State for African Affairs, speaking in South Africa at the start of a campaign to increase international pressure on Mugabe, said she hopes the incumbent "does the honorable thing and steps down."
Frazer joins a growing chorus of international voices criticizing the handling of Zimbabwe's presidential and parliamentary elections, CNN reported.
"My preferred option would be that the will of the people will be accepted," she said. "That Mr. Mugabe does the honorable thing and steps down."
She said challenger Morgan Tsvangirai won based on the reporting of the Zimbabwe Electoral Support Network and other independent monitors. A partial recount is under way.
"I think (Mugabe) is -- with this great delay in announcement -- trying to steal the election," Frazer said. "He is intimidating (the) population and election officials as well. (We've) also heard reports of the police stuffing ballots."