With his longtime coach Johan Bruyneel standing next to him, Armstrong said Landis seemingly pointed the finger at everyone still involved in the sport.
"We have nothing to hide," Armstrong said. "We have nothing to run from."
Landis was stripped of his 2006 Tour de France title for doping, yet always denied cheating until now. He recently sent e-mails to cycling officials and sponsors detailing his blood doping. He also claimed that Armstrong and Bruyneel paid an International Cycling Union official to cover-up a test in 2002 after Armstrong purportedly tested positive for the blood-boosting drug EPO.
In an e-mail Landis sent to USA Cycling chief Steve Johnson, he said Armstrong's positive EPO test was in 2002, around the time he won the Tour de Suisse. Armstrong won the Tour de Suisse in 2001, not 2002.
"We're a little confused, maybe just as confused as you guys," Armstrong said, with Bruyneel by his side. "The timeline is off, year by year."
The Wall Street Journal first reported the details of the e-mails.
Landis also implicated other cyclists, including longtime Armstrong confidant George Hincapie, and acknowledged using human growth hormone starting in 2003.
"Look forward to much more detail as soon as you can demonstrate that you can be trusted to do the right thing," Landis wrote in the e-mail to Johnson.
USA Cycling said it would comment later Thursday. Landis did not respond to messages left by the AP.