The FBI has confirmed a body found in Wyoming is missing woman Gabrielle 'Gabby' Petito, whose recent disappearance gripped the United States, with the local coroner saying she was murdered.

The Teton County coroner said the body found on Sunday was that of Ms Petito, and "initial determination for the manner of death is homicide. The cause of death remains pending final autopsy results," an FBI statement read.

US authorities launched a massive search for the 22-year-old when her family filed a missing person report on 11 September, after she mysteriously vanished during a road trip with her boyfriend.

Ms Petito quit her job and packed her life into a camper van for a cross-country adventure in July with her boyfriend Brian Laundrie, 23, documenting their journey in a stream of idyllic-seeming Instagram posts.

Mr Laundrie was declared a "person of interest" in the case and declined to cooperate with police.

The mystery deepened after he also went missing.

The FBI urged anyone with information about Mr Laundrie's "role in this matter or his current whereabouts" to contact them.

"The FBI and our partners remain dedicated to ensuring anyone responsible for or complicit in Ms. Petito's death is held accountable for their actions," said FBI Denver Special Agent In Charge Michael Schneider.

The couple embarked on their journey across the United States from New York, posting photos of magnificent views of the American West and the two of them smiling happily next to their small white van.

In one YouTube video published during their trip, they are shown kissing tenderly, enjoying a sunset together and strolling on a beach.

However, in August, police in Utah responded to a domestic violence report involving the couple.

Police body cam footage published by US media shows a distraught Ms Petito saying she had had an altercation with Mr Laundrie.

Speaking to a police officer after their van was pulled over, Ms Petito is seen crying and saying she struggles with mental health problems.

Ms Petito said she slapped Mr Laundrie after an argument, but added that she meant no harm.

The police officer decided no charges would be brought but ordered the couple to spend a night apart to calm down.