CONAKRY, Guinea (AP) — Guinea's opposition candidate Cellou Dalein Diallo declared himself the winner of the West African country's presidential election Monday before the official results have been announced, setting up a tense showdown with the incumbent leader of a decade.

The party of President Alpha Conde, who is seeking a controversial third term, swiftly condemned Diallo's declaration as “irresponsible and dangerous.”

In its statement the ruling party called on "the competent institutions to take all necessary measures to prevent disorder and to prevent any attempt to destabilize the country and its legitimate institutions.

Guinea’s national election commission, meanwhile, reiterated that only it could release official results and would do so by the end of the week.

Monday's development marked a dramatic escalation in an already tense electoral season. Conde's decision to seek another term by having the constitution modified already had led to protests that left more than 50 people dead this year.

Diallo said his declaration was based on information gathered at polling stations by his party, the Union of Democratic Forces of Guinea. He did not give any figures to back up his claim.

“Despite all the anomalies of this election ... and in view of the results that came out of the polls, I emerge victorious from this presidential election,” he told scores of cheering supporters who thronged his party's headquarters in the capital, Conakry.

Even before Diallo's announcement, Conde's government already was criticizing his opponent's intention to declare victory.

“This strategy of forced, premature and unjustified celebration was meticulously planned well before the election by Mr. Cellou Dalein Diallo,” the government's communications unit said in a press release Monday.

Observers fear the political standoff between Conde and Diallo could reignite long-standing ethnic tensions between Guinea's two largest ethnic groups. Conde draws his support from his Malinke community, while Diallo is heavily backed by the Peuhl ethnic group. Sunday marked the third time the two men have vied for the presidency, and previous electoral match-ups have seen bursts of intercommunal violence.

Tensions were inflamed during the election campaign so much that the United Nations chief urged Guineans to refrain from ethnic profiling and violence.

In a statement issued on the eve of the poll, U.N. Secretary-General Antonio Guterres “urged all political leaders and their supporters to refrain from acts of incitement, inflammatory language, ethnic profiling and violence.”

Conde came to power in 2010 in the country’s first democratic elections since independence from France in 1958. Many saw his presidency as a fresh start for the mineral-rich country mired by decades of corrupt, authoritarian rule.

Opponents, though, say he has failed to improve the lives of Guineans, most of whom live in poverty despite the country’s vast mineral riches. In his final campaign speech, Diallo condemned the country's high unemployment and human rights abuses of the past decade.

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Associated Press writer Krista Larson in Freetown, Sierra Leone, contributed to this report.