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, according to the Chelan County Sheriff's Office.

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

Decker, 32, was wanted on charges of kidnapping and first-degree murder, as reported by 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 them home in Wenatchee following a visit.

Authorities have stated that the girls died from apparent suffocation, with their wrists bound using zip ties.

Decker has a background as an ex-soldier and may have engaged in mountain survival training, which could explain his capability to remain undetected for an extended period.

The remains were found on Grindstone Mountain, just a few miles from where the girls' bodies were earlier discovered. A $20,000 reward had been announced by the US Marshals Service for information leading to Decker's capture, causing widespread closures of the national forest areas popular among hikers in the vicinity.