HARARE, Zimbabwe — Zimbabwe's main opposition leader said Saturday he respectfully rejects the court ruling upholding the president's narrow election win and called the inauguration set for Sunday "false," while U.S.-based election observers said the country does not yet have a "tolerant, democratic" voting culture.

Nelson Chamisa spoke a day after the Constitutional Court unanimously rejected the opposition's claims of vote-rigging in favor of President Emmerson Mnangagwa, saying it did not bring "sufficient and credible evidence."

Chamisa said "we have the right to peaceful protest" and that other routes will be pursued. "Change is coming," he said. "Political doors are going to be opened very soon." He gave no details.

Last month's peaceful election was seen as a chance for Zimbabwe to move on from Robert Mugabe's repressive 37-year-rule. Now Chamisa alleges "a new persecution" after a deadly crackdown on the opposition.

The 40-year-old opposition leader again said he won the election and that the southern African nation needs fundamental reforms that cannot be resolved by five more years of "vacant leadership."

The 75-year-old Mnangagwa, a former Mugabe enforcer who has tried to restyle himself as a reformer, appealed for calm after the court ruling and in a Twitter post told Chamisa "my door is open and my arms are outstretched."

Zimbabwe's electoral commission had declared Mnangagwa the winner of the July 30 balloting with 50.8 percent of the vote. It later revised it to 50.6 percent, citing an "error" but arguing it was not significant enough to invalidate the win. It said Chamisa received 44.3 percent.

Chamisa's opposition Movement for Democratic Change party late Friday issued an angry statement saying it soon would announce a "vigorous program of action in response to this electoral theft of the century."

Chamisa on Saturday, however, said he didn't know where the statement came from. He said the party's national council will meet next week on the way forward, and he did not directly respond to questions about the possibility of a government of national unity.

Mnangagwa, who took power in November after Mugabe stepped down under military pressure, called the election Zimbabwe's most transparent and credible ever. The government badly needed a credible vote to end its status as a global pariah, have international sanctions lifted and open the door to investment in the collapsed economy.

Final reports are pending from dozens of Western election observers invited for the first time in nearly two decades. They noted few issues on election day but expressed concern over "excessive use of force" that followed. Six people were killed two days after the vote when the military swept into the capital, Harare, to disperse protests.

Mnangagwa has said an inquiry would begin after his inauguration.

"The president must make it his priority to ensure these incidents are thoroughly investigated and those responsible brought to justice," Britain's minister for Africa said Saturday.

The new statement by the joint mission of the U.S.-based International Republican Institute and the National Democratic Institute noted the "acts of repression" against the opposition and said it was up to the people of Zimbabwe "to weigh the court's ruling in light of the overall electoral process to determine the credibility of the election."

The statement concluded: "Zimbabwe has not yet demonstrated that it has established a tolerant, democratic culture that enables the conduct of elections in which parties are treated equitably and citizens can cast their vote freely." A final report is yet to come.

Meanwhile, the 60,000-seat National Sports Stadium was being prepared for Sunday's inauguration, with soldiers drilling and workmen hanging colorful pro-Mnangagwa banners.

"Rest assured of a brighter tomorrow," one banner said.

Chamisa said he would not attend.