A band of hooded gunmen broke into a beach bungalow near Acapulco, Mexico, and raped six women tourists after tying up a group of men with their own cell phone cables, officials said Tuesday.
Another woman, who was also in the bungalow, was not attacked during the incident early Monday near the beach resort city.
The victims, who were Spanish nationals on vacation, are now under the protection of Mexican authorities. Spanish officials have also been notified.
Acapulco Mayor Luis Walton condemned the attack during a Tuesday news conference and vowed to apprehend those responsible.
"It's a very delicate situation," he said. "We are going to have the full weight of the law against those responsible."
He called the attack regrettable, apologized for it and said it would probably affect the image of Acapulco, known for its burgeoning tourism sector.
State prosecutor Martha Elba Garzon said her office would not reveal the names of the victims or anything more related to the investigation, but she vowed to uphold the "responsibility to provide security to tourists and our people."
Acapulco, in the state of Guerrero on Mexico's Pacific coast, is generally thought of as a relatively safe city despite rampant violence in the surrounding region. After a series of gruesome murders in Guerrero in recent years, American and British authorities issued travel warnings.
The U.S. State Department said resort city bars, including those in Acapulco, can be "havens for drug dealers and petty criminals."
But the agency said "resort areas and tourist destinations in Mexico generally do not see the levels of drug-related violence and crime reported in the border region and in areas along major trafficking routes."
Spain's Foreign Ministry also advises travelers that "while foreign tourists rarely are victims of kidnapping or extortion, they can be victims of assaults and robberies."
It said Guerrero "should especially be avoided," or travelers should proceed with "extreme caution."
"In Acapulco, organized crime has carried out violent incidents, although until now they have not affected foreign tourists or the places they frequent," the agency said.
An estimated 107,000 Spaniards live in Mexico and reside mostly in the capital.