Armstrong was banned for life in 2012 and stripped of his seven Tour de France titles for doping. He has suggested in interviews that he'd be willing to talk to the commission in return for a reduction of his ban.
Cookson, who was elected in September on promises of confronting the sport's drug-stained past, said his body had no power to reduce Armstrong's ban in return for him telling what he knows. But he conceded "there has to be some form of incentive" for some witnesses.
Any possible leniency for Armstrong from USADA would also have to be weighed against the opinion of WADA and the International Olympic Committee. IOC President Thomas Bach said he opposed any lessening and would be "very uncomfortable" with it.
Cookson said the commission would likely start work in early 2014 and he wanted to finish within 12 months.
Meanwhile, concerns over Jamaica and Kenya are still on the WADA agenda at its four-day summit, and the world anti-doping authority's board will examine its report from an audit of Jamaica's drug-testing program on Friday.
Jamaica Sports Minister Natalie Neita-Headley told delegates Thursday that her government would now give more money to the national anti-doping body after the revelations of a major breakdown in its testing program last year possibly one of the recommendations from the WADA report, which hasn't been made public yet.
Neita-Headley spoke of the country's "financial difficulties," and USADA said it has been asked for help by its Jamaican counterparts.
WADA has provided a copy of its report into the country's drug-testing breakdown to the Jamaican government and anti-doping officials and has asked for their feedback before any findings are announced following Friday's board meeting.
WADA also says it welcomes long-awaited moves this week by the Kenyan government to set up an investigation into allegations of widespread doping in the East African country's high-altitude training bases. Kenyan authorities had promised an investigation over a year ago.
In its main business in Johannesburg, WADA will vote on proposed changes to its anti-doping code on Friday, and is expected to bring in longer bans for serious dopers among other updates. The new code will take effect Jan. 1, 2015 and in time for the next Summer Olympics in Rio de Janeiro.
WADA is pushing for a doubling of bans for intentional doping offenses from two years to four, ensuring a doping cheat will miss at least one Olympics. That proposal, the most obvious deterrent being considered, appears to have widespread approval.
FIFA backs the move to four-year bans, although chief medical officer Jiri Dvorak said the world soccer body considered provisions for leniency for players who test positive for "social drugs" like marijuana were also important.
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