Fifty-seven Brazilian navy recruits were hospitalized over the weekend with respiratory problems whose cause has not been determined, officials said.

The recruits were taken to the Marcilio Dias Naval Hospital in Rio de Janeiro, where their relatives were allowed to visit them on Sunday.

The young men were subjected to extremely intense training and "abuse," Joao Luiz Pereira, the father of one of the sailors, said.

"You give your son to the navy and they return him sick," Pereira said.

The young men were infected with "a bacteria," the press reported, citing the relative of another sailor.

The sailors' families have asked military officials to explain what happened, but no reason has been given for the mass hospitalization.

The 57 young men were completing a training course for navy riflemen at the Admiral Milciades Portela Alves Training Center, where many of them started complaining of headaches and dizziness on Saturday.

The recruits were diagnosed with "symptoms of acute lack of respiratory capacity," the navy press office said.

Tests were done and doctors are awaiting the results, which should be available in the next few days, the navy press office said.

Two of the recruits, who were in the most serious condition, were taken to the intensive care unit, the navy press office said.