Two sisters from Texas and a friend are missing in Mexico after they crossed the border last month to sell clothes at a flea market, US authorities said Friday.

Maritza Trinidad Pérez Ríos, 47; Marina Perez Rios, 48; and her friend, Dora Alicia Cervantes Sáenz, 53, were riding in a green mid-1990s Chevy Silverado to a flea market in the city of Montemorelos, in the state of Nuevo León. It’s about a three-hour drive from where the sisters are in Peñitas, a small border town in Texas near McAllen.

Very few details have been released. The FBI said it «cannot provide comment on this ongoing investigation» and «relentlessly pursues all options when it comes to protecting the American people, and that doesn’t change when they’re in danger across the border.»

The fate of the three women, who have not been heard from for some two weeks, remains a mystery and has garnered relatively little publicity.

Peñitas Police Chief Roel Bermea said their families have been in contact with Mexican authorities, who are investigating their disappearance.

US Customs and Border Protection says the three women crossed into Mexico on February 24, according to Bermea. Peñitas is a few hundred feet from the Rio Grande.

The husband of one of the women spoke to her by phone while she was traveling through Mexico, the police chief said, but grew concerned when he was unable to reach her afterwards.

“Since he couldn’t make contact over that weekend, he came over that Monday and told us,” Bermea said. Nothing has been heard from the three women since then.

Bermea said the women were riding in a green mid-1990s Chevy Silverado to a flea market in the town of Montemorelos, in Nuevo León state. It is about a three hour drive from the border. Officials with the state attorney’s office said they have been investigating the woman’s disappearance since Monday.

Last week, four Americans on a road trip to Matamoros, in the Mexican state of Tamaulipas, were shot and kidnapped. Two members of the group died and two others have been returned to the US.

The friends had traveled to Mexico because a woman in the group was seeking a cosmetic procedure, a law enforcement official with knowledge of the matter told NBC News. The official said the cartel gunmen targeted the group in a case of mistaken identity.

The Gulf cartel apologized Thursday and five people were arrested Friday.

The government’s response and the search for the four Americans contrasts with efforts to locate 112,000 missing Mexicans across the country, many of whom are being sought only by their desperate relatives.