Two Texas sisters and their friend have not been heard from for about two weeks after going missing in Mexico.
Mystery surrounds what has happened to the trio who crossed the border on Friday 24 February to sell clothes at a flea market.
Maritza Trinidad Perez Rios, 47; Marina Perez Rios, 48; and Dora Alicia Cervantes Saenz, 53, were travelling in a green mid-1990s Chevy Silverado to the city of Montemorelos, in Nuevo Leon state.
Montemorelos is about three hours drive from where the sisters are from in Penitas, a small border city in Texas near McAllen.
Texas officials have advised Americans not to travel to Mexico at all during the spring break holidays and beyond because the country is deemed "too dangerous".
The husband of one of the missing women spoke to her on the phone while she was travelling in Mexico but became concerned when he couldn't reach her later, according to Penitas police chief Roel Bermea.
The senior officer added: "Since he couldn't make contact over that weekend, he came in that Monday and reported it to us."
It comes as four Americans were kidnapped by gunmen last week during a road trip to Matamoros, in the Mexican state of Tamaulipas.
Two people in the group were found dead while the pair who survived have now returned to the US.
The four childhood friends from North Carolina had driven to Mexico because one woman in the group had wanted a cosmetic procedure known as a tummy tuck from a Matamoros doctor, according to a relative.
Soon after reaching Mexico, they were caught in the crossfire between two groups of rival drug cartels.
Tamaulipas is one of six Mexican states which are on the US state department's 'do not travel' list. The others being Sinaloa, Zacatecas, Colima, Guerrero, and Michoacan.
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Meanwhile, it is currently spring break season where US college students will be on holiday, including in Mexico. They and other visitors to the country are being advised to continue exercising extreme caution.
'Significant safety threat'
The Texas department of public safety (DPS) has gone as far as urging Texans to avoid travelling to Mexico altogether during spring break, and beyond, due to the ongoing violence.
"Drug cartel violence and other criminal activity represent a significant safety threat to anyone who crosses into Mexico right now," said DPS director Steven McCraw.
"We have a duty to inform the public about safety, travel risks and threats. Based on the volatile nature of cartel activity and the violence we are seeing there; we are urging individuals to avoid travel to Mexico at this time."
There was widespread publicity over the kidnapping case, but the fate of the sisters and their friend has garnered relatively little attention.
The FBI has said it is aware the trio have gone missing. The bureau added it "relentlessly pursues all options when it comes to protecting the American people, and this doesn't change when they are endangered across the border".
The women's families are in contact with Mexican police who are investigating the disappearance of their loved ones.