The FBI has reached out to authorities in Mexico as they continue to hunt for Nancy Guthrie and her mysterious kidnapper, The Post has confirmed.

The police dragnet has been expanded well beyond Tucson as the halting investigation enters its third week, law enforcement sources said.

However, the sources also emphasized there is currently no evidence of cartel involvement

The confirmation follows claims from a supposed ransom note writer that the 84-year-old mother of Savannah Guthrie is being held “south of the border,” according to TMZ, which received the letter

Guthrie’s home in Tucson, Arizona, is around an hour’s drive to the Mexican border, prompting speculation that she may have been taken to Mexico after vanishing from her home on February 1.

The FBI had given no official confirmation that it is searching for Nancy in Mexico, however a person of interest was detained and questioned in the border town of Rio Rico on Feb. 10.

That person was soon released without charges, but the incident suggests authorities are considering the possibility that Guthrie was taken over the border after she was abducted on Feb. 1.

Security camera from Guthrie’s home caught a suspect apparently disarming the camera on the morning Guthrie went missing; the gloved, gun-toting suspect appeared to have facial hair behind a full-face ski mask

Follow The Post’s live updates on Savannah Guthrie’s missing mom

The FBI recently visited a Tucson gun shop and showed the owner names and photos of people who “looked Mexican,” the store’s owner, Phillip Martin, told The Post on Tuesday.

Most of the roughly 20 persons of interest had brown complections and facial hair matching the suspect’s.

In and around Tucson, the investigation — led by the Pima County Sheriff’s Department with help from the FBI — has hit dead end after dead end.

Authorities detained their first person of interest in the town of Rio Rico on the same day they released the camera footage, but they released the man less than twelve hours later with no charges.

Several days later, a SWAT team descended on a house near Guthrie’s neighborhood and questioned several people, although none were arrested.

A possible suspect’s DNA was found on a glove discarded near Guthrie’s home, yet this, too, appeared to have been a red herring after the sample failed to match anyone in the FBI’s national DNA database.

Authorities are currently testing another DNA sample recovered inside Guthrie’s home, the Pima County Sheriff’s Department confirmed on Wednesday.

Authorities have also employed a high-tech “Bluetooth sniffer” in an attempt to trace signals coming from Guthrie’s pacemaker.