Leftist government candidate Lenin Moreno has claimed victory in Ecuador's presidential vote on Sunday but the conservative challenger Guillermo Lasso, a former banker, has called for a recount and vowed to challenge the results.
Moreno secured 51.1 percent of the votes, compared with Lasso's 48.9 percent, with more than 96 percent of votes counted, according to the electoral council.
Lasso alleges fraud and has not conceded.
"They've crossed a line," Lasso told supporters in his coastal hometown of Guayaquil.
"We're going to defend the will of the Ecuadorian people in the face of this fraud attempt," he said.
No official winner has yet been declared.
Impacts of results
The results could be a relief for WikiLeaks founder Julian Assange. Lasso vowed to remove Assange from the Ecuadorian embassy in London if he won the runoff.
It would also boost the struggling leftist movement in South America after right-leaning governments recently came to power in Argentina, Brazil and Peru as a commodities boom ended, economies flagged and corruption scandals grew.
Allegations of fraud
Supporters of Lasso have taken to the streets in protest at the unofficial result, alleging electoral fraud.
Hundreds of Lasso supporters swarmed in front of electoral council offices in the capital, Quito, and Guayaquil, chanting "No to fraud!" and "We don't want to be Venezuela!"
Isolated clashes were reported but protests lost intensity as the night progressed and people went home.
Venezuela's President Nicolas Maduro congratulated Moreno on his win, assuming it confirmed, as did Bolivia's President Evo Morales.