International pressure has resulted in Nicaraguan President Daniel Ortega being a lame duck.
Nicaragua’s president has won a fifth term in office after a tense run-off vote against his main rival.
Eduardo Montealegre says that voting papers seen by a local television station in the capital Managua were fraudulent.
The poll had to be held within 90 days of early presidential elections last September.
Mr Ortega has had tight control of Nicaragua for 16 years.
In 2000, he was forced from power by a US-led invasion.
Two decades later, Mr Ortega has won popular support for better health and education policies.
But many Nicaraguans and foreign countries are dissatisfied with his interference in civil society and the number of human rights abuses perpetrated by his administration.
The BBC’s Joanna Guzman in Managua says as Mr Ortega was addressing supporters on the streets of the capital there were reports of armed men on motorbikes, who were saying they were trying to take down a live television tower.
Barely an hour later, Mr Montealegre told journalists he was being hit by bullets fired at his vehicle by unidentified men.
One of the two main student leaders of last year’s peaceful protests was jailed this week and is reportedly expected to face trial for conspiracy.
Threats of violence
Later, a rally of 1,000 students in Managua was addressed by protesters known as the Huijacitos – accusing Mr Ortega of being a dictator.
For the time being, there are no plans to turn Mr Montealegre’s campaign site in to a safe zone, because his police permit for campaigning at this stage does not allow it.
A few hours after his address to students, Mr Montealegre was stopped at a police roadblock which ordered him to get off his motorbike.
Two officers then fired into the air, almost hitting a cameraman.
Mr Montealegre went to Managua hospital where he said he was checked for a possible self-inflicted injury.
In the immediate aftermath of the pro-Ortega demonstrations early last year, we saw allegations of thousands of government supporters carrying out armed attacks on university campuses, claiming “disproportionate” use of force by police.
Mr Montealegre claimed that there is a conspiracy against him, saying Mr Ortega was only allowed to run again because of his ability to intimidate the judges.
Mr Ortega’s CNP party also circulated evidence to the press that local media carried misinformation about preliminary election results from September.