Ecuador, Sept. 3: Ecuadorian authorities announced Friday the release of 50 guards and seven police officers who were taken hostage for more than a day, in what the government described as a response by criminal groups to its efforts to regain control of several large correctional facilities in the South American country.

The country's corrections system, the National Service for Attention to Persons Deprived of Liberty, said in a statement that the 57 law enforcement officers —who were held in six different prisons — are safe, but it didn't offer details about how they were released.

Early Friday, criminal groups in Ecuador used explosives to damage a bridge, the latest in a series of attacks this week. Nobody was injured in the explosion.

Government officials have described the violent acts as the work of criminal gangs with members in prisons responding to efforts by authorities to retake control of several penitentiaries by relocating inmates, seizing weapons and other steps.

Four car bombs and three explosive devices went off across the country in less than 48 hours. The latest explosion with dynamite happened early Friday on a bridge linking two cities in the coastal province of El Oro, National Police commander Luis García told The Associated Press.

Hours earlier, a domestic gas tank with wads of dynamite attached exploded under a different bridge in Napo province of Napo, located within Ecuador's portion of the Amazon rainforest.

Consuelo Orellana, the governor of Azuay province, reported early Friday that 44 of the hostages at a prison in the city of Cuenca had been released. The country's correction system said later that all 57 were freed.

Security analyst Daniel Pontón said the chain of events, which took place three weeks after the slaying of presidential candidate Fernando Villavicencio was a "systematic and clearly planned" attack that had shown the state was ineffective in preventing violence. (AP)