The Financial Supervisory Authority in Stockholm said it will take action against companies that sell the risky, complex instruments to retail investors who don’t understand what they’re getting into, according to a statement on Monday.

The FSA, which also opened the door to greater regulation for the area, said such instruments are "unsuitable for most, if not all, consumers."

Exchange-traded crypto-tracking products exist in Europe and a Bitcoin ETF opened in February in Canada. But in the U.S., regulators have so far fought them amid concerns over potential manipulation and liquidity.

The warning from Sweden’s financial watchdog comes amid a surge in the price of Bitcoin. Sweden is home to the largest Bitcoin exchanged-traded product: The USD 1.7 billion Bitcoin Tracker EUR, which invests in swap contracts to mirror the cryptocurrency’s returns, is listed on the Stockholm Stock Exchange.

Sweden’s FSA has previously warned about the risks of investing in crypto assets, but also acknowledged it has little power to supervise them.

The watchdog began its review of tracker instruments last year. While the market is subject to more regulation, the FSA said the current requirements don’t do enough to mitigate the risks buyers face.

When retail buyers of volatile instruments follow the market, "the risk of large losses increases," the FSA said.

Bitcoin tops USD 48,000 for the first time after Tesla's purchase 

Blackrock takes first step into crypto exposure in two funds 

Danes start new investment fund: Plan to trade cryptocurrencies from Cyprus