The police said that the American victim had severe swelling around her nose, and that her companion, 23, had been hit in the area around one of his eyes. The woman left Brazil after registering the crime and undergoing preliminary medical treatment, while her companion remained here, where he is cooperating with the police, said Alexandre Braga, a senior police investigator with Rio’s special police unit for crimes involving tourists.

The two men who were apprehended over the weekend were arrested after investigators tracked purchases made with the victims’ credit cards, which were stolen by the assailants, and examined images obtained from security cameras at a filling station and convenience store where the men had stopped to buy energy drinks and whiskey.

After news of the arrests was broadcast Sunday night on Fantástico, a widely viewed news program on the Globo television network, other people here came forward to tell the police that they recognized the assailants in connection with other crimes, largely robberies, aboard what appeared to be the same transport van. One 21-year-old Brazilian student said she had similarly been held for an hour and raped by the same men on March 23, after boarding the van.

The revelation of that previous episode seemed to have shaken the public security forces here. The victim had quickly registered the case with the police, but the authorities were said to have slowly investigated the claim. Two police officials in charge of investigating the March 23 case were abruptly removed from their posts on Monday.

Brazil has recently grappled with other high-profile cases of gang rape, including one episode in 2012 in Queimadas, a city in the northeast Paraíba State, in which six men were convicted of raping five women at a birthday party. Two of the women were killed after recognizing their attackers.

More broadly, reports of rape in Brazil have climbed significantly since 2009, when the nation’s criminal code was changed to expand the legal definition of rape to include crimes involving anal penetration. More than 5,300 people, about 90 percent of whom are women, registered cases of rape in the first six months of 2012, an increase of more than 150 percent since 2009.

Ms. Gonçalves, the federal official in charge of combating violence against women, said much of the increase in reports of rape involved efforts to encourage victims to report the crimes. “Women are more courageous about coming forward with what happened to them than in the past,” she said.