US television presenter Savannah Guthrie believes her mother was kidnapped and that two ransom notes demanding money were real, but more information is needed to find her kidnapper.

Nancy Guthrie, 84, was last seen at her home near Tucson, Arizona, on 1 February. Investigators believe she was taken against her will, but have not arrested a suspect.

In her first interview since the disappearance, Savannah Guthrie recounted the moment she learned her mother was missing and wrestling with the painful idea that her fame may have made her mother a target.

"To think that I brought this to her bedside, that it's because of me," the NBC host said. "I'd just say: 'I'm so sorry, Mommy. I'm so sorry.'"

Guthrie, who made the remarks in an interview on NBC's Today show, described the shock she felt on what had otherwise been a regular February day.

"My sister called me. I said, 'Is everything OK?' And she said, 'No.' She said, 'Mom's missing,'" Savannah Guthrie said. "And I said, 'What? What are you talking about?' She said, 'She's gone.' And she was in a panic. I was in a panic.'"

Family members had found doors propped open at Nancy Guthrie's home when they arrived to check on her.

Her mother's mobile phone, purse and other personal effects were still in the house, despite the doors being open.

Initially, she said, the family believed Nancy Guthrie may have had a medical episode in the night and paramedics had come through the back doors of her home to care for her mother.

But when Savannah Guthrie and other family members called local hospitals, Nancy Guthrie was nowhere to be found.

Her doorbell camera - which has become a fixture of the investigation - had been removed from the front door.

"It just didn't make any sense," Savannah Guthrie told her former Today show co-host Hoda Kotb in the emotional interview.

During the investigation, police released images of a masked person captured by a security camera at Nancy's Guthrie's home before she was taken.

Days later, the FBI said two ransom notes were sent to TMZ and local news outlets.

It remains unclear if authorities believe the ransom notes are authentic.

The television presenter said that before the kidnapping, her mother was in "tremendous pain" and described how she had trouble walking.

"She can't wander off," she said.

During one of the more emotional moments of the interview, Savannah Guthrie described grappling with whether her mother was taken because of the television host's fame.

This month, Pima County Sheriff Chris Nanos, who is leading the investigation, said authorities believe Nancy Guthrie was "targeted", and they know the motive. But the sheriff declined to publicly say what it is, citing the ongoing investigation.

In the interview broadcast on Thursday, Savannah Guthrie described the immediate aftermath of her mum's kidnapping as "a blur". She said she, her brother and her sister spent their days praying for answers and crying for their mother.

She temporarily stepped away from her morning-show presenting duties after the disappearance and was not part of NBC's coverage of the Winter Olympics as planned. She is expected to return to work, but it's unclear when.

The family has indicated that they believe Nancy Guthrie may no longer be alive, but Savannah Guthrie said: "We need to know."

The Guthrie family is offering a $1m reward, in addition to $100,000 pledged by the FBI, for information leading to Nancy Guthrie's return. (BBC)

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