In a display of unexpected unity, the International Olympic Committee president Juan Antonio Samaranch yesterday appeared alongside the senior official who has made the most serious allegations of corruption in the Games' 100-year history.

Swiss lawyer Marc Hodler shook the Olympic movement to its core when he alleged that four "agents", including one IOC member, had been involved in vote-buying over the past 10 years. He cited supposed irregularities in the elections of at least four Olympic cities - Atlanta, Nagano, Sydney and Salt Lake City.

Samaranch sat grim faced at a press conference in Lausanne as 80-year-old Hodler, the longest-serving member of the IOC and a part of its powerful ruling executive board, repeated his vote-buying charges and said his life had been shaken since his initial accusations on Saturday.

Looking tired and drawn, Hodler, who is due to step down from the IOC shortly, said: "These have been the three worst days I have spent in my long career in sport. In times of crisis, you get to know who your friends and who your enemies are."

China, still bitter at its failure to win the right to stage the 2000 Games, called for the "purity" of the Olympic movement to be upheld in its first reaction to the sleaze scandal and claimed it had lost its bid to Sydney for non-sporting reasons.

Sydney beat China by only two votes in 1994 for the 2000 Games and China has continually hinted that it had been unfairly treated.

Samaranch, who has headed the IOC since 1980 when among the candidates he defeated was Hodler, compared the crisis to the boycotts of the 1980s and the Ben Johnson drug scandal at the 1988 Seoul Games. "They were difficult moments, and now we are facing another difficult moment," he said. "I am sure that we will solve this problem."

Samaranch said the investigation would centre on Salt Lake because it is the only case with documented evidence. "If there is other proof, we will open other cases," he said. "If there are cases of corruption, we can't permit it in the Olympic family."

Hodler repeated his defence of the Salt Lake City scholarship programme but claimed they had been blackmailed during their bid to stage the 2002 Winter Games. The Salt Lake bid committee operated a fund that provided nearly £400,000 in aid to 13 people, including six relatives of IOC members.

"For us, Salt Lake City was a victim of blackmail and not a villain," Hodler said. "The real villains are the agents who put the cities in awkward positions using blackmail. Salt Lake City had been forced by blackmail to give financial favours."

Hodler said the "most detestable agent" has approached cities which were involved in bids claiming that "never in the past 15 years has a city won the games without his help". He said other agents promise to secure IOC votes for free, while demanding £3 million if the city wins the bid.

Hodler is in charge of the IOC ethics committee which draws up the rules on bidding. Critics have long argued that there should be sanctions against IOC members who accept the inducements offered to them by bidding cities. As long ago as the 1980s angry bidding cities complained to Samaranch about the unacceptable demands of certain IOC members. Peter Norman, the 1968 Olympic 200 metre silver medallist who was involved in Melbourne's unsuccessful campaign for the 1996 Games said bribery had existed for so long that IOC members expected "inducements" when they visited a bidding city.

"Corruption can be as small as a souvenir pin or the stuffed animals which are handed out," Norman said. "It doesn't surprise me a bit that someone from the inside has made that allegation."

Hodler came under attack for making the allegations only when he is about to retire. He said he decided to go public after a senior Swiss government official asked him about rumours of misconduct and wondered whether Hodler had been bribed to keep quiet.

Until now, there has only been "hearsay" of bribery that would not stand up as evidence in court, Hodler said. He admitted he had heard complaints from previous unsuccessful Olympic bidders, including Manchester and Stockholm. "But now there is written proof of corruption practices in the case of the Salt Lake fund," he said.