(Updates with ARD reaction, details)

LONDON, Jan 30 (Reuters) - The entire board of Thailand’s weightlifting federation has resigned less than a month after allegations of doping by child weightlifters were made in a German TV documentary.

The mass resignation was announced by president of the Thai Amateur Weightlifting Association, Boossaba Yodbangtoey, in a Jan. 30 statement seen by Reuters.

German broadcaster ARD’s recent documentary about doping in weightlifting ‘Secret Doping – the Lord of the Lifters’ had forced longtime International Weightlifting Federation president Tamas Ajan to stand aside temporarily for 90 days as the IWF launched an investigation into allegations of corruption.

The International Olympic Committee expressed concerns over the doping and corruption allegations. Ajan has denied any wrongdoing.

The German broadcaster also secretly recorded Thai weightlifter Siripuch Gulnoi, who admitted to taking banned substances before winning a bronze medal at the London 2012 Olympic Games.

“The journalist neither identified his real name nor shown his real profession,” Boossaba Yodbangtoey wrote in the resignation letter. “Ms Gulnoi was not aware of being filmed by the TV journalist at all.”

Investigative reporter Hajo Seppelt, who co-authored the ARD documentary said reporters had indeed gone undercover in order to get the information.

“In order to reveal the truth about massive doping in Thai weightlifting we had to act as undercover reporters otherwise the athlete would have never admitted what she did on camera,” Seppelt told Reuters.

“Everything is in full length, unedited and in original voice. We have been asked by anti-doping entities for the material.” (Additional Reporting by Karolos Grohmann Editing by Christian Radnedge)