Nigeria's World Cup warm-up friendly against Scotland in London on Wednesday is the subject of a match-fixing investigation by Britain's serious crime squad.

The National Crime Agency, which investigates serious and organised crime, is said to have asked world football's governing body FIFA to issue an alert over attempts to influence the game at Fulham's stadium Craven Cottage.

The NCA are said to have told FIFA they have general information from Asian betting markets suggesting there had been attempts to rig the friendly and they hope to stop any suspect activities by issuing the alert.

A FIFA spokesman said they worked closely with law enforcement agencies and other sports organisations to tackle match manipulation, and encouraged anyone with information to contact their integrity hotline or confidential reporting system.

FIFA was aware of the reports, the spokesman said, adding: "We are not in a position to comment or provide information on any match-manipulation investigations that are ongoing so as not to compromise investigations, nor do we provide any comments as to whether or not any investigations are under way."

Stewart Regan, the Scottish Football Association chief executive, said: "We have been liaising with the NCA and FIFA, and will be preparing for the match as normal."

Newspaper reports said there was no suggestion that any players were involved.

Nigeria's coach and players said they were stunned by the suspicions surrounding the Scotland friendly.

"We're not part of this. We don't know anything about this. We're here to play," coach Stephen Keshi told Sky Sports News.

Striker Peter Odemwingie, based in England with Premier League side Stoke, added: "This is the first time I'm hearing it. I'm with the players every minute, every day, we don't hear of this."

A spokesman for the NCA said that while it would "from time to time provide operational detail" in a bid to reassure the public, "it does not routinely confirm or deny the existence of specific operations or provide ongoing commentary on operational activity."

In recent months, the NCA has been investigating allegations in English lower-league football of spot-fixing, where specific events in a match are pre-arranged.

The issue of match-fixing is returning to the spotlight ahead of the World Cup, with pre-tournament warm-up matches said to be prime targets for match fixers acting on behalf of illegal betting syndicates in Asia.

Ralf Mutschke, FIFA's head of security, was quoted in The Daily Telegraph newspaper as saying the organisation was presuming that the World Cup in Brazil was "under threat".

The Times quoted him as saying the group phase was more "vulnerable" than the final, when players were less likely to be swayed.

A spokesman for British bookmaker William Hill said they had seen no evidence of the issues surrounding the friendly and would not expect to.

"This sort of activity will be executed in the illegal betting market, and is unlikely to be seen in the UK or European regulated sector," the spokesman said.

A spokesman for competitors Coral added: "We are not aware of any unusual betting patterns on this match, and that has been reflected across the industry.

"However we are not complacent about it. We do know that where there is integrity concern over football matches, betting tends to take place far from British shores."

The London match is scheduled as a home fixture for Nigeria, who are finalising their World Cup preparations.