"We are at an hour of desperation, and we need your help," she says in the video posted on Instagram.

Nancy Guthrie disappeared in the middle of night from her home in Tucson, Arizona, and was last seen on 31 January. Authorities believe she was taken against her will. The FBI is offering a $50,000 (£36,000) reward for information.

The Monday deadline of 17:00 local time (00:00 GMT) has since passed, and the FBI says they are not aware of "any continued communication between the Guthrie family and suspected kidnappers".

A previous alleged deadline for ransom, which is meant to be paid in Bitcoin, passed on 5 February.

Nancy Guthrie was discovered missing when she did not attend a Sunday church service on 1 February and other members grew concerned.

The family has released three previous videos saying they were willing to speak to the potential kidnapper, and asking to provide proof that her mother was alive.

The family had earlier indicated that they would be willing to pay for her safe return.

"I just want to share a few thoughts as we enter another week of this nightmare," Guthrie says, appearing alone in the latest video, in contrast to previous recordings where she has appeared with her siblings. "She was taken, and we don't know where. And we need your help," Guthrie says.

She thanks the public for their prayers, saying that her mother is also feeling them "even in this darkest place".

She requests people everywhere, "even if you're far from Tucson", to report anything suspicious that could lead to clues about her mother.

She asks, "if you see anything, if you hear anything, if there's anything at all that seems strange to you, that you report to law enforcement".

Investigators say that no suspects, persons of interest or vehicles had been identified in the case.

In an update just before Monday's deadline, the Pima County Sheriff's Office said it did not have any new information to release publicly.

The sheriff's statement added that the "investigation into Nancy Guthrie's disappearance remains active and ongoing", and that "the FBI is handling all aspects related to any ransom note(s) or communications involving the Guthrie family".

The FBI also released a statement, saying that FBI agents from around the country "continue to deploy to Tucson".

"We are currently operating a 24-hour command post that includes crisis management experts, analytic support, and investigative teams. But we still need the public's help," the FBI statement added, including the number for the FBI's tip line.

'We will pay': Savannah Guthrie's new message about missing motherAt a news briefing last week, FBI Special Agent Heith Janke said his agency was reviewing a ransom note sent to several media outlets.

The note gave a deadline for payment of 17:00 on Thursday, he said, without specifying which time zone, and had a second deadline for Monday.

On Monday, FBI Director Kash Patel arrived in Tucson, on a trip that was scheduled prior to Guthrie's disappearance.

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