Robert Mugabe has won Zimbabwe's presidential election with 61 percent of the vote, compared to 34 percent for his challenger and Prime Minister Morgan Tsvangirai, elections officials said.
The Zimbabwe Electoral Commission results, announced on Saturday, showed Mugabe's Zanu-PF party won 158 of the 210 parliament seats, giving it a two-thirds majority that enables it to make amendments to the new constitution and existing laws.
The results were declared after Tsvangirai's Movement for Democratic Change (MDC-T) announced at a news conference that it "totally rejects the election".
Tsvangirai, who has called the elections a "farce", told a news conference on Saturday in Harare, the capital, that he would exhaust all legal remedies to challenge the election outcome.
The MDC leader said his party would not participate in any government resulting from what he called a "fraudulent" election.
Originally named the MDC, the party's name carries 'T' for Tsvangirai after a breakway faction formed a rival party called MDC-N whose leader, Welshman Ncube, was one of the candidates in the July 31 elections.
"There is national mourning in the country," Tsvangirai said shortly before Mugabe was declared the victor. "We will go to court."
The United States said the results were the culmination of a deeply flawed process and did not represent the will of the people.
"In light of substantial electoral irregularities reported by domestic and regional observers, the United States does not believe that the results announced today represent a credible expression of the will of the Zimbabwean people," John Kerry, the US secretary of state, said in a statement.
The European Union said it was concerned about alleged irregularities and a lack of transparency in the elections.
Al Jazeera's Azad Essa, reporting from Harare, said there had been many reports of increased police presence and roadblocks in the capital.
"There is a lot of disappointment in the city, with many MDC supporters devastated by the result," he said.
"They are convinced the results have been manipulated, and so there is a lot of confusion and anxiety about what happens next.
|Olusegun Obasanjo, head African Union mission in Zimbabwe, talks to Al Jazeera
"One of the things that many people are wondering [about] is how this victory will affect the economy and their lives."
Roy Bennett, treasurer of the MDC-T, called on Saturday for a campaign of "passive resistance" against Mugabe, as another opposition leader accused the 89-year-old president's Zanu-PF party of electoral fraud.
The conduct of the elections prompted the resignation on Saturday of a leading ZEC commissioner, Mkhululi Nyathi.
"I do not wish to enumerate the many reasons for my resignation, but they all have to do with the manner the Zimbabwe 2013 Harmonised Elections were proclaimed and conducted," Nyathi, a senior lawyer in Bulawayo, Zimbabwe's second-largest city, was quoted as saying by the local media.
Simba Makoni, leader of the Mavambo Kusile Dawn (MKD) political party, said that the electoral process had been "engineered" to make Mugabe president.
"Zimbabweans must brace themselves for more suffering," Makoni, a former finance minister, said.
However, former Nigerian President Olusegun Obasanjo, who heads the AU's vote monitoring mission, said on Friday that flaws in the electoral process had not stopped the will of the people from being expressed.
"We justified that by the process which led to the election itself, it was free," he said.
But the mission is asking election authorities in Zimbabwe to investigate reports that large numbers of eligible voters were turned away from polling stations.