A 24-year-old woman from Oaxaca, Mexico, had been walking for five or six days west of Nogales when her smuggler pulled her away from their group in late June and raped her while the rest of the crossers slept.

A Honduran woman said the man she paid to get her across the border raped, robbed and threatened to kill her in April.

Although all unauthorized immigrants are at risk of abuse, women and children — particularly children traveling without a parent — are especially vulnerable. That is particularly concerning to human rights groups and law enforcement officials this summer, as the recent surge of unaccompanied minors and women traveling with their young children has brought tens of thousands of potential victims to the border.

Human rights organizations estimate that as many as 6 in 10 women experience sexual violence during their journey to the United States. But few report it — some may be embarrassed, others afraid. And if they manage to come into the country without being caught, many prefer to continue their journey rather than risk being deported if they go to the authorities, Santa Cruz County Sheriff Tony Estrada said.

“What we receive and report and what really happens, there’s probably a big separation between those two,” Estrada said.

So far this year, the Santa Cruz Sheriff’s Office has taken 11 reports of sex offenses, one of which was a sexual assault on an immigrant.

Last year, three of 23 cases involved women border crossers. One involved a 14-year-old girl, also from Oaxaca, who was found by Border Patrol agents in a remote spot east of Arivaca and said she was raped by her smuggler. The case against the alleged rapist is still pending.

In the last decade, Customs and Border Protection has seen an increase in sexual violence against migrants as drug smuggling organizations have taken over the smuggling of people, agency spokesman Andy Adame said. The threat of sexual assault is so high that in Altar, Sonora, a popular staging area for border crossers about three hours from Tucson, pharmacy shelves are lined with more than a dozen brands and types of birth control.

The Department of Health and Human Services’ Office of Refugee Resettlement has reported an increase of pregnant teens, and about 27 percent of the unaccompanied minors in its custody are girls. But officials don’t know if the teens are getting pregnant before or during their journeys, said Jennifer Podkul, senior program officer with the Women’s Refugee Commission, a national organization that advocates for laws, policies and programs to improve the lives and protect the rights of refugee and internally displaced women, children and young people.

“This is something we’ve been hearing about for years,” Podkul said. “But because more women are coming, the issue is getting more attention.”

The risk for sexual violence doesn’t start at the U.S.-Mexico border. Podkul has heard stories of migrants being kidnapped in Mexico to extort their relatives in the United States and being raped while they are held captive.

The biggest dangers for migrants today are kidnapping, extortion and rape. Twelve percent of migrants surveyed in a recent University of Arizona study said they were robbed by bandits during their last crossing, while seven percent said they had been kidnapped — almost half of them by their coyote or guide.

In the first seven months of fiscal year 2013, the latest data available, the Border Patrol’s Tucson Sector had reports for four sexual assaults, 29 physical assaults and 26 robberies involving border crossers.

Border crossers are easy victims, because not only are they being led through more remote areas, but coyotes also have more power over them, said Fernando Valdez, deputy consul with the Mexican Consulate in Nogales.

The two recent cases reported to law enforcement are in the minority. In the incident involving the woman from Oaxaca, she reported it to the Border Patrol when they processed her. The woman said the perpetrator fled when a helicopter flew overhead, leaving the entire group behind. Her group walked for a few more days before agents caught them.

In the case of the Honduran woman, her alleged rapist, a Mexican national, was caught and turned over to Mexican authorities for prosecution. Officials with the Sonora attorney general’s office have not responded to repeated requests for information regarding the status of the case.

Even when victims do come forward, their attackers are hardly ever brought to justice.

“Most of the cases we get, the victim doesn’t even know the smuggler,” CBP spokesman Adame said. “They haven’t been with them for an extended period of time. They only give a vague description of the person, don’t know his name. Those guys are hard to track down.”