A double medallist from North Korea was this morning expelled from the Olympic Village after testing positive for drugs.

Kim Jong-su won silver in the 50m pistol event and bronze in the 10m air pistol. But in an in-competition dope test - which the International Olympic Committee has been conducting for all medallists here - Kim was found to have taken the illegal beta-blocker propranolol.

A three-man disciplinary panel met this morning and stripped him of his medals. It led to China's Zonglian Tan being promoted to the 50m pistol silver, with Vladimir Isakov now taking the bronze. The air pistol bronze now goes to the US's Jason Turner.

"Propranolol is a beta-blocker and banned in certain events, the precision sports such as shooting and archery," said Professor Arne Ljunqvist, the chairman of the IOC's medical commission.

"This was found in Kim's system. I interpret that it was a deliberate intake because of the importance it has in that sport. The consequences are obvious."

Kim's positive test was the second of these Games after the Spanish road cyclist Maria Isabel Moreno was stripped of her Olympic accreditation on Tuesday. The IOC also declared a third incident, involving the 59th-ranked artistic gymnast Thi Ngan Thuong Do, from Vietnam, who was found to have taken the diuretic furocemide and also expelled from the Games.

Ljunqvist had more sympathy for Thi, whose drug test was for a substance that is used to control pre-menstrual tension. He explained that she was likely to have been ill advised on what to avoid and what she could take.

With only three tests so far during this Olympics, Ljunqvist was claiming triumph for the IOC's doping policy. When asked if the relatively low number of positive tests might suggest that the dopers are beating the system, he said: "The evidence shows we are ahead of the cheats. My interpretation is that three positive tests is fairly low.

"You would expect six or seven tests. This is a feature of increased awareness in the sports population. The figures are encouraging rather than showing anything else."

Ljunqvist explained what the IOC considers to be an effective testing information system developed over the past seven years by the World Anti-Doping Agency, whose health, medical and research committee he chairs. But there remains scepticism about the efficacy of the testing regime at the Beijing Games, with a Polish swimming coach labelling the tests of some Chinese swimmers "irrational".

The IOC was indignant. "I don't think officials should enter into speculation like that and unfairly question the achievements of athletes in Beijing," said Ljunqvist. "It is not fair, particularly from people who have official positions in national teams."