Federal officials say homicide has been ruled out in the continuing investigation of a Thursday morning explosion that claimed a man's life this week along U.S. 26 on Mount Hood.

"The blast appears to have been an isolated incident and there are no indications of links to terrorism," U.S. Forest Service spokeswoman Laura Pramuk said in a news release Friday.

Federal authorities believe the blast was caused by a "substantial" amount of material that target shooters use to make exploding targets. The explosion occurred off the highway and on National Forest Service land.

Parts of a gun were found at the scene, Pramuk said.

She also said it might take several weeks to verify the man's identity because additional testing might be required.

Dr. Karen Gunson, with the Oregon Medical Examiner's Office, declined to release the man's name Friday. She confirmed that the man died of "blast injuries and body fragmentation."

With homicide ruled out, that leaves officials to determine whether the death was a suicide or an accident.

About 6:30 a.m. Thursday, the U.S. Forest Service reported an explosion roughly six miles east of Welches and near Milepost 48, bringing in federal agents, the Metropolitan Explosive Disposal Unit and dozens of local police. When investigators converged on the scene, they found a white car parked along the highway and a gaping hole in the ground.

They deployed an armored blast-resistant robot to explore the site for additional explosives, but none was found.

The blast occurred about 25 feet from the road and just inside the woods, according to the Forest Service. It left a hole about 11 feet wide.

Several companies make binary explosive target kits, which are commonly available at gun stores. Generally, they need to be mixed with an oxidizer and fuel before they become volatile. The mixture is then placed in a can or a jar that will explode when hit by a bullet.

The kits, widely available on the Internet, require no background checks or proof of identity to buy, have no storage requirements and aren't regulated as an explosive.

Brian Bennett, a spokesman with the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives in Seattle, declined to speculate how much of the explosive material was used to create such damage during Thursday's blast.

The FBI initially took the lead on the investigation, then gave the reins to the ATF. The ATF determined that the explosion didn't violate federal codes controlling explosives and turned the investigation over to the Clackamas County Sheriff's Office.

As authorities combed through the scene Thursday, U.S. 26 was closed in both directions for about 12 hours. Federal investigators also descended on a Northeast Portland address within hours of the incident.

They cordoned off a two-story fourplex in the 8500 block of Northeast Halsey Street. Neighbors reported seeing investigators taking items out of one of the units, which had the same address as the registration of the car found near the scene of the explosion.

-- Rebecca Woolington and Rick Bella

503-294-4049; @rwoolington