France and Germany's finance ministers and head bankers have called on G20 leaders to intervene in the murky world of cryptocurrencies such as bitcoin, ethereum and litecoin.
A letter to fellow G20 finance ministers, signed by German interim finance minister Peter Altmaier, France's Bruno le Maire, Banque de France's Francois Villeroy de Galhau and the Bundesbank's Jens Wedimann, said digital "currencies" could "pose substantial risks for investors".
It argued that the increasingly popular cryptocurrencies needed coordinated regulation, and that a discussion on the subject should be tacked on to the agenda for this year's G20 Summit in Argentina.
The letter warned that cryptocurrencies were "largely mislabeled as 'currencies' in the media and on the internet", following on from a similar statement from the European Central Bank yesterday.
The head of the UK's Financial Conduct Authority, Andrew Bailey, has also warned that the cryptocurrencies in no way resemble traditional currencies such as sterling or the dollar.
Finance heads are worried that the large amounts of money being ploughed into bitcoin and its peers, and the lack of understanding of how they work, could be a risk to financial stability.
The value of bitcoin surged last year, but in more recent weeks has taken a dramatic tumble.