Leftist flag-bearer Salvador Nasralla conceded shortly after Honduras' key ally Washington endorsed President Juan Orlando Hernandez's re-election, following a month of sometimes deadly street clashes.
"With the decision by Washington, I am no longer in the running," Nasralla told the HCH television station. As he spoke, police were dismantling the latest barricade erected around the capital by his supporters to protest the vote.
Washington is Honduras' main aid donor and largest trading partner and US diplomats have been following events in the impoverished Central American republic nervously since the November 26 election.
But today the US State Department congratulated the 49- year-old on his re-election, with the proviso that all "irregularities" in the vote be fully investigated.
More From This Section
"A significant long-term effort to heal the political divide in the country and enact much-needed electoral reforms should be undertaken," spokeswoman Heather Nauert said.
"We urge Honduran citizens or political parties challenging the result to use the avenues provided by Honduran law."
Nauert noted that vote monitors from both the Organization of American States and the European Union had noted shortcomings in the way the election had been conducted.
Washington urged all Hondurans to refrain from violence and warned that government security forces who fail to respect the rights of peaceful protesters must be held to account.