Olympic and world champion swimmer Sun Yang's short suspension for a doping violation in May was "appropriate", a senior Chinese anti-doping official said on Monday, defending the delayed announcement and lenient punishment.

The China Anti-Doping Agency announced on its website on Monday that Sun tested positive for the stimulant trimetazidine at an in-competition doping test during the national swimming championships on May 17.

Sun was then suspended from competition for three months and stripped of the 1,500m freestyle title he won at the national meet by the Chinese Swimming Association, which also fined him 5,000 yuan ($815).

Sun competed at the Incheon Asian Games in September winning three gold medals and one silver after the ban expired on Aug 16.

Sun's short suspension and CHINADA's late announcement sparked widespread debate.

"Sun submitted legitimate evidence, in a hearing after the test, that proved he used the substance for medical treatment of a heart condition not to deliberately enhance his athletic performance," Zhao Jian, deputy director of CHINADA, told China Daily on Monday.

"This case met the World Anti-Doping Agency's punishment-reducing requirements, but Sun was still counted responsible for not declaring medicines he was taking beforehand, so imposing a three-month ban was appropriate."

Trimetazidine, a drug for cardiac diseases, was listed by the World Anti-Doping Agency in January as a prohibited "specified stimulant", which is considered more susceptible to inadvertent use and can carry reduced penalties.

Zhao said WADA only banned athletes from taking the substance during competitions, which means Sun's long-term medication during training was legal.

Sun posted a statement about the doping violation on his personal micro blog account on Monday evening.

"For whatever reason, an athlete should be responsible for any substance taken, so I fully accepted the punishment and had made deep reflections on my mistake. Swimming is my life. I will train harder and control myself more strictly from now on to pay back my supporters with more glories," he said in the statement.

In response to the timing of the announcement, Zhao said CHINADA's heavy workload from May to October, during which it handled about 9,900 tests for the Nanjing Youth Olympics and Asian Games, delayed the analysis and statistical procedures.

But not everyone accepts this explanation.

"The swimming association issued the light punishment hurriedly in the swimming offseason before Sun's violation was even reported. It couldn't be more obvious that it was to protect him," said a sohu.com report on Monday.

Neither Sun nor the swimming association was available for further comment on the punishment.

Earlier this year, in February during the Sochi Winter Olympics, Ukrainian cross-country skier Marina Lisogor also failed an in-competition doping test for trimetazidine and was expelled from the Games.

"Athletes and coaches should take the recent cases as a wake-up call for better anti-doping education and more sensitive medication precaution," Zhao said.

(For the latest China news, please follow @PDChina on Twitter at http://www.twitter.com/PDChina and @PeoplesDaily on Facebook at http://www.facebook.com/PeoplesDaily)