The FBI has released the first physical description of the man believed to have kidnapped Nancy Guthrie, the mother of US news anchor Savannah Guthrie.

Nancy Guthrie, 84, disappeared in the middle of the night from her Tucson, Arizona home and was last seen two weeks ago. Authorities believe she was taken against her will.

The FBI has analyzed footage from a doorbell camera outside her home and believes she was kidnapped by a male who is between 5ft 9in (175cm) and 5ft 10in tall, with an average build.

This is the first time the man in the video has been officially identified as a suspect in the case, which has drawn a significant amount of attention both in the US and abroad.

In its latest statement, the FBI confirmed that they established identifying details after conducting a forensic analysis, highlighting a backpack worn by the suspect, identified as a 25-litre Ozark Trail Hiker Pack.

A pair of black gloves has also been found during the search for Guthrie, according to CBS.

Nancy Guthrie was last seen on the evening of Saturday, January 31, when family members dropped her home. Members of her church noticed her absence at Sunday’s service and alerted her family.

Authorities have warned that Nancy may be in dire health without her medication. Pima County Sheriff Chris Nanos stated she is not in good physical health but has no reported cognitive issues.

Since February 1, the FBI has received more than 13,000 tips in connection to the case, including 4,000 within 24 hours after the footage was released. They have now doubled the reward for information leading to her safe return from $50,000 to $100,000.

Earlier this week, a man was detained in connection with Guthrie's disappearance after his home in Rio Rico, south of Tucson, was searched, but he was released shortly afterward. He reported he did not know who Nancy Guthrie was.

Savannah Guthrie and her two siblings have made several social media pleas directed at their mother's potential abductors, expressing their belief that she is still alive and their willingness to pay for her return.