FIFA will monitor the World Cup's most vulnerable games for match-fixing threats.
FIFA legal director Marco Villiger said Friday the final group-stage games present the highest risk of being fixed, especially those that involve teams that already qualified for the second round or have been knocked out.
The 32 World Cup teams play their third matches from Tuesday through next Friday.
"We use our means to keep our focus on these matches. Anything else would be naive," Villiger said.
FIFA's monitoring of legal and illegal betting markets suggests the World Cup has been "clean and clear" so far, with no suspicious wagering patterns identified.
"What we see is clean, but this does not mean we see everything," Villiger said.
No player, referee or team official has yet called a special hotline FIFA created for this tournament to report being approached by fixers, he said.
Villiger said any alert could prompt a FIFA match official to visit the locker room before kickoff to warn teams their match was under suspicion.
FIFA regards match-fixing by illegal betting syndicates as the biggest threat to soccer's integrity -- a danger that has grown since the last World Cup in Germany. Police currently are working with UEFA to probe suspected fixing of more than 200 matches involving teams from at least 12 countries.
"If you had asked me in 2006, I would not have believed that the World Cup could be the goal of the betting mafia," Villiger said.
FIFA has since created a company called Early Warning System, which monitors global betting patterns with more than 400 licensed bookmakers.
In recent months, FIFA has built closer ties with global police agency Interpol and is building a network of informers. The biggest challenge is to penetrate the illegal betting markets run by southeast Asian organized crime gangs.
"We realized that only the monitoring is not enough," Villiger said. "In the investigation side, there is definitely room for improvement.
"If we have indications that something happened in the qualifiers, then we would definitely go into this," said Villiger, adding that a disciplinary case could be opened for any FIFA competition match from the previous 10 years.
"We could sanction this team and expel them, possibly from further tournaments."