The FBI has asked anyone who may have seen the missing children of Lori Vallow in Yellowstone national park to come forward with photos or videos to help investigators.

Seventeen-year old Tylee Ryan and her seven-year-old brother JJ Ryan have been missing since September. Their mother, 46, was arrested in Hawaii last month and has been extradited to Idaho, where the children were living and where she was due to appear in court on Friday, charged with child abandonment.

Divorce documents filed by her deceased ex-husband reportedly claimed Ms Vallow believed she was "a god assigned to carry out the work of the 144,000 at Christ's second coming in July 2020". She and her current husband, Chad Daybell, were both involved in an Idaho-based group that promotes preparing for the apocalypse, or biblical end times.

The bizarre case spans several states and includes investigations into three mysterious deaths.

Now, federal authorities have released images showing the children at the popular nature reserve on 8 September. Further pictures showed the silver Ford F-150 pickup truck the family was travelling in with Ms Vallow's brother, Alex Cox.

The FBI hopes that people who visited the park on 8 September may have captured images of the family and that this may assist officers in the investigation.

The new photo was recovered from Ms Vallow's Apple iCloud and is the last known image of Tylee Ryan, CBS News reported. ​

Members of the public can upload any relevant photos to a website set up by the FBI at at fbi.gov/rexburg.

Investigators asked the public to continue reporting tips in the case to the Rexburg Police Department at (208) 359-3000 or the National Centre for Missing and Exploited Children at 1-800-843-5678 (1-800-THE-LOST).