Embattled Tour de France icon Lance Armstrong on Wednesday angrily brushed off fresh doping allegations that emerged in a magazine report.

Armstrong is the subject of a federal investigation in the United States following allegations of doping levelled by disgraced former teammate Floyd Landis, who was stripped of his 2006 Tour de France title for doping.

A fresh report claims to substantiate Landis's accusations.

American magazine Sports Illustrated made several allegations against Armstrong in a website report on Tuesday, including one that said Armstrong once used a hard-to-detect blood boosting drug, HemAssist, to boost his performances in the late 1990s.

Armstrong successfully battled cancer in 1998 and returned to the sport to win the world's biggest cycle race seven times.

The American, who is set to retire after the Tour Down Under this week, brushed off the fresh doping claims before the start of the race's second stage on Wednesday.

"I don't have anything to say," he said when asked to respond to the report, which he said he had read.

"I've perused it. There's nothing there."

In 2010, Landis launched a series of damning allegations against Armstrong, with whom he rode in the US Postal team for several years, claiming the American had used banned substances throughout his career.

Armstrong has never tested positive and has rejected all allegations of doping. He also claims Landis is not a reliable witness because he has confessed to being a drugs cheat.

Landis attempted a recent comeback to the sport but on Tuesday announced his retirement, claiming doping was still widespread and would be nearly impossible to eradicate.

On Landis's decision to retire, Armstrong said: "Got nothing to say about that either."

When pressed on Sports Illustrated's claims, he hit back: "Dude, are you that stupid? Which part of 'I'm not commenting' is not clear to you?"

Armstrong said: "I don't have anything to worry about on any level."

The Sports Illustrated report claimed it had "new information" about Armstrong, having "reviewed hundreds of pages of documents and interviewed dozens of sources in Europe, New Zealand and the US".

The report cited another former member of Armstrong's old team, Motorola, New Zealander Stephen Swart, who told the magazine the Texan was the driving force behind some of the team members deciding to use the banned blood booster EPO (erythropoietin) in 1995.

"He was the instigator," Swart is quoted as saying in the report.

"It was his words that pushed us toward doing it."

Armstrong is widely credited with one of the greatest comebacks in the world of sport and his Livestrong foundation - which raises money and awareness in the global fight against cancer - is followed by millions.