The United States Anti-Doping Agency is bringing new charges against Lance Armstrong, the country's most famous and successful professional cyclist.
In a 15-page letter, the agency said its investigation included evidence dating back to 1996 and accused Armstrong of a "pervasive pattern of doping" over many years.
The agency says it has evidence from more than 10 colleagues and team employees who witnessed Armstrong taking the performance enhancer EPO, testosterone and having blood transfusions.
He has been immediately banned from competing in triathlons - a sport he took up after his retirement in 2011 from cycling following a 25-year sparking career.
Armstrong, 40, who won the Tour de France seven times in a row, never failed a drugs test, but has been the subject of persistent allegations, the BBC reports.
He has always denied taking drugs and called the new charges "baseless and motivated by spite".
"I have been notified that USADA ... intends to again dredge up discredited allegations dating back more than 16 years to prevent me from competing as a triathlete and try and strip me of the seven Tour de France victories I earned," Armstrong said in a statement.
The allegations against him include previously unpublicised claims of doping in 2009 and 2010, reports say.
Armstrong could face a lifetime ban and be stripped of his awards if he is found to have used performance-enhancing drugs.
In February this year, federal prosecutors in the US dropped an investigation into allegations of doping at a team partly owned by Armstrong.