In a statement, the firm explained that:

"Pending clarification of the scope and enforceability of the Wire Act and applicability of State and Federal laws to online gambling by US citizens, William Hill has today taken steps to cease accepting casino and poker business from clients with a US address or US issued credit card."

"Such steps are already in place to prevent internet sports betting by US domiciled individuals."

The move follows accusations levelled at the chairman of Sportingbet, Peter Dicks, by the Louisiana authorities, who have accused him of "gambling by computer", thereby violating the state's morality laws.

Three other arrest warrants were issued against Sportingbet executives, and the Louisiana police force reportedly plan to spread their net still wider in the coming weeks.

Mr Dicks's legal team is arguing that he has not been to Louisiana in more than two decades, and could not, therefore, have committed a crime in the state.

Speaking ahead of a hearing to decide whether Mr Dicks should be extradited to Louisiana, Sportingbet's finance director, Andy McIver - set to assume the role of chief executive in October - announced that:

"We have now formally said that no board member is to go to the United States following the arrest of Peter Dicks."