Colorado officials are reviewing the death of journalist Hunter S Thompson, 20 years after it was ruled a suicide, at the request of his widow.

Thompson died at the age of 67 at his home in Woody Creek, Colorado, a small town north of Aspen, in February 2005.

The Colorado Bureau of Investigation said on Tuesday that it was conducting a "case review" of the 2005 investigation into his death, though the agency said this was not as a result of new evidence.

"By bringing in an outside agency for a fresh look, we hope to provide a definitive and transparent review that may offer peace of mind to his family and the public," Colorado Sheriff Michael Buglione said.

He added that Thompson had had a "profound impact" on his community and beyond.

Thompson was a renowned writer and journalist who wrote for dozens of outlets including Rolling Stone, Playboy, and ESPN.

His 1971 novel, Fear and Loathing in Las Vegas - a semi-autobiographical story about the counterculture of the 1960s - was later adapted into a film starring Johnny Depp.

Other books he penned include Hells Angels and Generation of Swine.

Colorado officials said they did not have a timeline for the investigation into Thompson's death and would provide an update once it was complete.

Thompson died of a self-inflicted gunshot wound while speaking on the phone with his wife.

His son later found his body in the kitchen, according to news reports.

An investigation into his death found no evidence of foul play.