Fifa widens World Cup bidding inquiry
Proceedings have already been opened against two executive committee members as part of a probe into votes allegedly being sold to stage the 2018 World Cup.
And investigations are also ongoing in relation to other Fifa officials who may have been involved.
But Fifa is also to probe any "alleged agreements between member associations" bidding for the 2018 and 2022 events.
England, Russia, Spain/Portugal and Netherlands/Belgium are all bidding for the right to host the 2018 World Cup and will find out who has won on 2 December.
The hosts of the 2022 World Cup will also be decided on the same day, with the United States, Australia, Qatar, Japan and South Korea all in the hunt.
"I'm not commenting on anything," US Soccer Federation president Sunil Gulati, chairman of the US Bid Committee, told BBC Sport.
"We're staying away from commenting on this. Hopefully they'll get to the bottom of all this pretty quickly," added Gulati.
England and the US initially asked to be considered as hosts for either the 2018 or 2022 World Cup. But on Friday, the Americans withdrew from the 2018 race, while England did the same for 2022.
The 2018 and 2022 decision will be made by Fifa's 24-strong executive committee.
See www.bbc.co.uk for full version.