Human remains, believed to be of a man wanted on suspicion of murdering his three daughters, aged nine, eight, and five, have been found in the US state of Washington.

Police had been searching for Travis Decker since officers found his phone and the bodies of his girls Paityn, Evelyn, and Olivia in a remote campground on June 2. His truck was also found nearby.

While positive identification has not yet been confirmed, preliminary findings suggest the remains belong to Travis Decker, the Chelan County Sheriff's Office stated on Thursday.

The remains were discovered in a remote wooded area south of the town of Leavenworth, Washington.

Decker, 32, was wanted on kidnapping and first-degree murder charges, according to Washington's Wenatchee Police Department, and officials believed he had been hiding in a remote part of the mountainous state.

The girls' mother reported them missing on May 30, after Decker failed to return his daughters to her home in Wenatchee, Washington, following a visit. He also did not take her phone calls.

Authorities said the girls died from apparent suffocation, and their wrists had been bound with zip ties.

Decker, an ex-soldier, may have gone off-grid as part of his military training, with reports saying he would disappear for weeks at a time.

The remains were found on Grindstone Mountain, a few miles from where Decker's daughters' bodies were located in June. A $20,000 reward had been announced by the US Marshals Service for information leading to Decker's capture.

The search had caused widespread closures of national forests popular among hikers in the area.