Image copyright Office of George HW Bush Image caption Sully the dog sleeps next to the casket of the late US President George HW Bush

The labrador who worked as a service dog for President George HW Bush has been pictured resting beside his coffin, in a moving tribute.

Mr Bush, who served as the 41st US president between 1989 and 1993, died late on Friday at the age of 94.

Sully the dog is travelling with the casket on the flight from Texas to Washington and back this week.

Mr Bush's body is due to lie in state this week ahead of a day of national mourning.

The coffin is being flown from Texas to DC on board Air Force One - temporarily renamed Special Air Mission 41, in homage to the late president - and then back on Wednesday, with Sully accompanying the body throughout.

Media playback is unsupported on your device Media caption George HW Bush's final journey to Washington DC

The picture was tweeted by Mr Bush's spokesman, Jim McGrath, showing Sully next to Mr Bush's casket on Sunday along with the caption: "Mission complete."

Image copyright Reuters Image caption Sully travelled with the coffin to Washington on Monday

Image copyright AFP/Getty Image caption He will make the return trip to Texas on Wednesday

Social media users thanked Sully for his services and commented on his and dogs' loyalty generally towards their owners.

Sully is named after the airline pilot Chesley "Sully" Sullenberger, who landed a passenger jet on the Hudson River in 2009, saving all 155 passengers and crew on board.

The two-year-old labrador was assigned earlier this year as a service dog to Mr Bush who used a wheelchair in the last years of his life.

A highly trained dog, Sully can perform a number of commands, including opening doors and fetching items such as the phone when it rings.

He will now work as a service dog, assisting with therapy for wounded soldiers.

Sully has his own Instagram account; here he is shown "assisting with voting" as Mr Bush cast his ballot in last month's US presidential mid-term election.

Not all US presidents have been fond of dogs, though: John F Kennedy was allergic to dogs, and Donald Trump does not have one.

President Bush had been receiving treatment for a form of Parkinson's disease and had been admitted to hospital with a blood infection in April.

He died in Houston, Texas.

He will be buried at the presidential library in Texas, alongside his wife of more than 70 years, Barbara Bush, who died seven months ago.