US TV host Savannah Guthrie has said her family is "at an hour of desperation" in the search for her missing 84-year-old mother - as the deadline on a ransom note draws nearer.

In a video posted on social media on Monday, Savannah Guthrie, co-anchor on NBC's Today show, called the saga a "nightmare" and pleaded to anyone with information to come forward.

"We believe our mum is still out there," she said.

"She was taken and we don't know where. And we need your help...

"If you see anything, if you hear anything, if there is anything at all that seems strange to you, that you report to law enforcement.

"We are at an hour of desperation. We need your help."

Her mother Nancy Guthrie was last seen at her own home near Tucson, Arizona, on the evening of 31 January, and was reported missing the next day after she did not turn up at church.

Law enforcement officials have concluded that the 84 year-old was kidnapped but no suspects have been identified, authorities have said.

A ransom note requesting the Guthrie family pay $6m (£4.4m) gave a deadline of Monday at 5pm MT (12am GMT) - a development that prompted Savannah Guthrie and her siblings to say over the weekend they would be willing to pay for their mother's return.

But authorities have not yet confirmed the authenticity of the note.

The FBI and Pima County Sheriff's Department are investigating the case, with the FBI offering a reward of up to $50,000 for information.

Read more:
Nancy Guthrie: What we know about mysterious disappearance
Savannah Guthrie tells mother's potential kidnappers 'we will pay'

Investigators said they were searching for a vehicle or vehicles that may be connected to her case.

Blood found on the front porch of Nancy Guthrie's home was a match to her, while her doorbell camera was disconnected in the early hours of Sunday morning, Pima County sheriff Chris Nanos has said.

Authorities said they have growing concerns about Nancy Guthrie's health because she requires daily medication.

She is believed to have a pacemaker and has experienced high blood pressure and heart issues, according to sheriff's dispatcher audio on broadcastify.com.