A domestic group of observers, Let's Have Democracy, said it recorded 600 complaints of voting irregularities, a handful of injuries in protests and 30 arrests.
Gadea, election observers and oppositions groups raised questions about the validity of the vote, as did the United States.
State Department spokeswoman Victoria Nuland repeated U.S. concerns over whether the elections were transparent and free of intimidation, violence and harassment.
"There are quite a number of reports, and we're concerned because the conditions weren't good going in," Nuland said. "And frankly, if the Nicaraguan government had nothing to hide, it should have allowed a broad complement of international monitors."