The value of Bitcoin has dropped below $6,000 – the lowest level since mid-November.
The digital currency fell as low as $5,920 on Tuesday – down 13% on the previous day – before recovering slightly, according to Bitstamp Exchange.
Bitcoin surged in value during 2017, starting the year at around $900 and topping $20,000 in December.
But it has since tumbled sharply, dipping below $8,000 on Friday amid worries about a global regulatory clampdown.
In the UK, Theresa May has said Britain should take a serious look at digital currencies such as Bitcoin because of the way they can be used by criminals.
Lloyds Banking Group and Virgin Money have banned customers from using credit cards to buy Bitcoin and other cryptocurrencies.
Lloyds said it had taken action on fears that some credit card customers are gambling on making big profits and overlooking the fact they will be laden with debt if the price falls.
Customers will still be able to buy digital currencies with debit cards, the banking group said.
Virgin Money also confirmed it had taken the same stance.
RBS, which also includes Natwest, said it kept the situation under review all the time but it was currently allowing credit card purchases along with Barclays.
The move by Lloyds follows warnings by regulators and ministers in the US, South Korea, China, Russia, India, Germany and France over the market.
Meanwhile, Facebook recently banned adverts for Bitcoin and other cryptocurrencies on its sites after criticism from users about scams and hoaxes being promoted in their newsfeeds.