Mr Mugabe was inaugurated at the State House in Harare shortly after 5 p.m. amid pomp and ceremony, but lacking the customary presence of many foreign diplomats.
The inauguration will allow Mr. Mugabe to attend an African Union summit opening Monday in Egypt with what he and his ruling ZANU-PF party will present as a fresh mandate.
The Zimbabwe Electoral Commission said Mr. Mugabe won 2.15 million votes or around 85% of the ballots cast in Friday's election, which was preceded by weeks of political violence that primarily targeted members of the opposition Movement for Democratic Change, which said scores of its supporters died from beatings and shootings by ZANU-PF militants.
Opposition leader Morgan Tsvangirai, who pulled out of the run-off on June 22, received some 233,000 votes while more than 130,000 ballots
were spoiled, the commission said.
Mr. Mugabe's inauguration was organized at top speed and went ahead at State House late Sunday afternoon, as correspondent Sylvia Manika reported.
Reports said Mr. Mugabe invited Tsvangirai
to attend the inauguration, but that Tsvangirai shunned the event, describing it as illegitimate.
But Tsvangirai told reporter Blessing Zulu of VOA's Studio 7 for Zimbabwe that no invitation reached him - and any such invitation would have been "an act of insolence."
Delegation chief Marwick Khumalo said hate speech,
incitement to violence and war rhetoric instilled fear in the electorate while statements by senior officials made it hard to dismiss claims the violence
was state-sponsored, as Irwin Chifera reported.
Mr. Mugabe's critics renewed calls for international action against his government.
Kenyan Prime Minister Raila Odinga said the African Union should deploy troops in Zimbabwe to help resolve the crisis. South African Archbishop Desmond Tutu said there was a "very good argument" for an international force to restore peace in the country. Tutu called on the A.U. to send a “powerful signal” by unanimously rejecting a new Mugabe administration.
But A.U. officials said Sunday that sending troops or peacekeepers to Zimbabwe is not likely. African foreign ministers meeting in the Red Sea resort of Sharm-el-Sheikh, Egypt, called on Saturday for dialogue between Zimbabwe's government and the opposition.
A.U. officials said Zimbabwe is not officially on
the agenda of the summit opening Monday, when Mr. Mugabe is expected to join the heads of state and government in summit.
For more on the atmosphere in sharm-el-sheikh ahead of the official opening, reporter Chinedu Offor spoke with VOA correspondent Peter Heinlein.
Political analyst Zenzo Nkomo said Mr. Mugabe could be in for a surprise at the summit, as a growing number of African leaders are distancing themselves from his style of rule.