The state Herald newspaper carried the remarks after a briefing Mugabe gave to Zimbabwean reporters at the end of last week’s summit of the continentwide African Union.
U.S. Embassy officials in Zimbabwe and Ethiopia, where Assistant Secretary of State Johnnie Carson is visiting, would not comment on the remarks.
According to the Herald paper, Mugabe said nothing came out of those talks.
"You wouldn’t speak to an idiot of that nature. I was very angry with him, and he thinks he could dictate to us what to do," Mugabe was quoted as saying.
He said regional leaders supported the formation of a power-sharing government in February and then "you have the likes of little fellows like Carson saying ‘do this, do that.’"
"Who is he? I hope he is not speaking for Obama. I told him he was a shame, a great shame being an African American," Mugabe was quoted as saying.
Prime Minister Morgan Tsvangirai, head of the former opposition, visited President Barack Obama in Washington last month as part of a trip to the United States and Europe to re-engage with Western leaders after a decade of Zimbabwean isolation.
Mugabe is known for vitriolic outbursts against his critics, reserving some of his harshest comments for those who, like Carson, are black.
Mugabe labeled Carson’s predecessor, Jendayi Frazer, who also is black, as "that little girl trotting around the globe like a prostitute" to campaign against him.
Frazer had criticized Mugabe’s party over political violence and vote rigging surrounding disputed national elections in March 2008.
The pro-Mugabe state media launched repeated attacks against former U.S. Ambassador James McGee, who also is black, describing him as a "house Negro" for white Western leaders.
In typical language used by Mugabe, he has called former British Prime Minister Tony Blair a "B-Liar."
Before Tsvangirai joined the coalition government, Mugabe had referred to him as "Fatcheeks" and a tea boy, a lowly domestic worker.
On Friday, McGee, whose left Zimbabwe Sunday after a three-year tenure, promised more U.S. support for the country’s political and economic recovery but said democratic reforms needed to be in place first.
McGee, a harsh critic of Mugabe’s autocratic rule, rejected the idea that Zimbabwe needed more support from donors to restore the rule of law, respect for human rights and to guarantee basic freedoms of speech and association.
"It doesn’t cost anything … to have judges apply the law equally. Dropping phantom politically motivated prosecutions is free. Stopping the arrests of political activists and independent journalists is also free," McGee said in a farewell speech.