London - Olympic champion LaShawn Merritt was cleared to defend his 400-metre title in London next year after the American won his appeal Thursday against an IOC rule banning doping offenders from the games.

The Court of Arbitration for Sport invalidated the International Olympic Committee rule that bars any athlete who has received a doping suspension of more than six months from competing in the next summer or winter games.

The three-man CAS panel said the rule, adopted in 2008, was "invalid and unenforceable" because it amounted to a second sanction and did not comply with the World Anti-Doping Agency code.

It said the rule amounted to a "disciplinary sanction" rather than a matter of eligibility.

Merritt, the American 400-metre gold medallist in Beijing, had been ineligible under the IOC rule to compete in London even though he completed his doping ban earlier this year after testing positive for a banned substance found in a male-enhancement product.

The U.S. Olympic Committee challenged the rule and was backed by several other national Olympic and anti-doping bodies.

The IOC maintained it had the right to decide who is eligible to take part in its games.

The IOC said Thursday it "fully respects" the CAS verdict and will comply with it. However, the IOC said it would push for the rule to be included in a revised WADA code in 2013.

The CAS decision means Merritt becomes eligible to compete in London, as do other athletes around the world who have been affected by the rule.

"We're obviously happy about that," USOC CEO Scott Blackmun said.

"LaShawn made an error that he even amitted was a silly error. We're glad he's going to be able to compete."

The verdict against the IOC also opens the door for athletes in Britain to challenge a British Olympic Association rule that bans drug offenders for life from the games.

Among those affected by the British ban are sprinter Dwain Chambers, a former European 100-metre champion who served a two-year ban in the BALCO scandal, and cyclist David Millar, who also was suspended for two years for use of EPO.

"The IOC has a zero tolerance against doping and has shown and continues to show its determination to catch cheats," the IOC said in a statement.

"We are therefore naturally disappointed since the measure was originally adopted to support the values that underpin the Olympic Movement and to protect the huge majority of athletes who compete fairly.