LONDON - Formula One's governing body has banned teams from sending drivers coded messages under a controversial clampdown on the use of radio communications from this weekend's Singapore Airlines Singapore Grand Prix.

The International Automobile Federation (FIA) issued a follow-up on Monday to a technical directive sent to teams last week in which it gave more information about what they could and could not do during a race weekend.

Banned items on the list, provided to the media by the FIA's Formula One delegate, included "any message that appears to be coded".

Teams were told that the use of pit boards for such messages was also banned.

Other no-nos were answering a direct technical question over the radio from a driver, such as "am I using the right torque map?", and information about the level of fuel saving needed.

The changes, after 13 of 19 races, has caused some concern about safety implications as well as the impact on fans, who will now hear less chat between drivers and their teams.