MIAMI, United States -- Apparent human remains were found on Wednesday in a Florida nature reserve where authorities have been searching for the missing boyfriend of murdered road-tripper Gabby Petito, the FBI said.

FBI special agent Michael McPherson said personal items belonging to Brian Laundrie, who has been named a "person of interest" in Petito's murder, had also been found in the Carlton Reserve near Venice, Florida.

"Earlier today, investigators found what appears to be human remains along with personal items such as a backpack and notebook belonging to Brian Laundrie," McPherson told reporters.

"These items were found in an area that up until recently had been under water.

"Our evidence response team is on scene using all available forensic resources to process the area," he said. "It's likely the team will be on scene for several days."

Police have been searching for the 23-year-old Laundrie for weeks, and live television images on Wednesday showed search teams and sniffer dogs at work in the sprawling nature reserve.

The body of Petito, 22, lay in the wilderness of the western US state of Wyoming for up to a month before it was found in mid-September. According to the coronor, she had been strangled.

Petito had quit her job and packed her life into a camper van for a cross-country adventure with Laundrie, starting in July, documenting their journey in a stream of social media posts.

In images shared by the couple online they are all smiles -- barefoot in a canyon or surveying the ochre rocks of state and national parks.

- Argument in Utah -

But police in Utah revealed one disturbing incident after the young woman's disappearance -- a domestic violence report involving Petito and Laundrie in August.

Police bodycam footage shows a distraught Petito saying she had had an altercation with Laundrie.

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

Petito said she slapped Laundrie after an argument, but 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.

Petito's family filed a missing person report on September 11 after she mysteriously vanished, and Laundrie, her fiance, returned home to Florida without her.

Laundrie was subsequently declared a "person of interest" in the case. He declined to cooperate with police before vanishing himself.

Petito's death and the subsequent disappearance of the chief suspect sparked a blizzard of media coverage both in the United States and around the world.

It also triggered debate over the disproportionate attention accorded to missing white women.