The United Nations called Sunday for "transparency and promptness" in a vote recount in Ecuador to determine who will square off against the frontrunner in a second round of presidential elections.

The country's top electoral body said Friday it would conduct a partial recount of last week's first voting round following a request from the two candidates battling for second place.

Environmental lawyer Yaku Perez and right-wing former banker Guillermo Lasso finished neck-and-neck in the race to face leftist economist Andres Arauz in April's runoff.

The UN office in Ecuador said in a tweet Sunday it "trusts that the electoral authorities will act with efficiency, transparency and promptness, thus ensuring the timeliness of the electoral calendar."

The National Electoral Council (CNE) has said it would recount six million votes, representing about 45 percent of those cast.

Perez, 51, had been given 19.38 percent of the vote, just behind conservative Lasso, 65, who got 19.74 percent.

Pre-election polls had placed Lasso comfortably in second place but Perez performed far better than expected. 

Perez has since alleged wrongdoing in the first round, and said a recount would offer a chance "to demonstrate to the country that there is no fraud, that the electoral process was transparent."

Lasso supported the proposal.

Arauz, a 36-year-old protege of former socialist president Rafael Correa, led with 32.7 percent -- not enough to win outright and avoid a runoff.

Incumbent President Lenin Moreno's term in office ends on May 24. He did not seek re-election.