Toure already had alleged that the Saturday vote was marred by ballot-stuffing, vote-tampering and the creation of more than 50 fake polling stations charges the government denied.
Guinea has not had a legislative election since 2002, and repeated delays over the years have been accompanied by periodic violent protests, sometimes resulting in deaths.
Initially results had been expected within 72 hours. However, the electoral commission later said the 72-hour window would only begin when it had received all the ballots, a process still not complete nearly a week later. Helicopters were being used to spirit ballots from remote forested areas of the country.
Guinea held its first democratic presidential election in 2010 after decades of military and strongman rule. Although the vote was thought to be transparent overall, it showcased a deep divide between the country's Malinke and Peul ethnic groups, each of which represents about 40 percent of the population. Voters overwhelmingly backed politicians from their own groups the Malinke supported the winner, Alpha Conde, while the Peul backed Cellou Dalein Diallo.
The international community played a key role in mediating disputes leading up to the weekend vote, with the United Nations sending a special envoy for talks.
The opposition ultimately agreed to go ahead with the vote despite reservations about how it would be conducted, including concerns over the composition and role of the electoral commission as well as voter lists, said Vincent Foucher, an analyst with the International Crisis Group.
"They're very frustrated with the whole electoral process. They feel like they've been pushed into the election by the international partners, and they've been forced to accept conditions that they have issues with."
Foucher said the immediate catalyst for the opposition's announcement Thursday may have been the results announced Wednesday night, which showed Conde's ruling party winning in areas the opposition had expected to carry.
Yaya Kann, director of operations for the electoral commission, said the opposition's announcement would have no effect on the work of the commission, and that more provisional results would be published Thursday night.
President Conde has appealed for calm, saying that political debate must leave the street and take place in parliament.
"After the election, there will be nothing. The state is there to maintain order," he said Wednesday. "We will strengthen the police forces ... so that they are ready to act. We will strengthen the military battalions."
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Corey-Boulet reported from Dakar, Senegal.