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 huge amount of attention both in the US and abroad.

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

A pair of black gloves were also found during the search for Guthrie, reported CBS.

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

Officials have warned she may be in dire health without her medication. Pima County Sheriff Chris Nanos stated she was not in good physical health but had no reported cognitive issues.

Since February 1, the FBI has received more than 13,000 tips regarding the case, including 4,000 in the 24 hours following the release of the doorbell camera footage.

The FBI has increased the reward for information related to Nancy Guthrie's disappearance, doubling it from $50,000 to $100,000.

Earlier this week, a man was detained in relation to Guthrie's disappearance and his home in Rio Rico was searched before he was released. He claimed he did not know who Nancy Guthrie was.

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