Bitcoin prices fell below the $4,000 mark for the first time in a month Wednesday as investors continue to dump the cryptocurrency following a crackdown on fund raising in China and accusations of fraud from one of Wall Street's most influential leaders.

Bitcoins were marked at $3,970 each on the Bitsmap exchange in London, the lowest since Aug 13 and down some 5% from last night's levels following a series of disparaging comments from JPMorgan Chase & Co. (JPM) CEO Jamie Dimon, who called the virtual currency concept a "fraud" and said he'd fire any of his traders for dealing in it. So far this month, however, bitcoin prices have fallen nearly 20%, or more than $1,000, from the all-time peak the virtual currency reached on Sept. 1. 

"The currency isn't going to work," Dimon told the Delivering Alpha investor conference in New York. "You can't have a business where people can invent a currency out of thin air and think that people who are buying it are really smart."

"My daughter bought a bitcoin and it immediately went up, now she thinks she's a genius," Dimon said. "It's just not a real thing," Dimon said. "Eventually, it will be: 'the emperor has no clothes'."

It's been a tough few weeks for the coins, which first came under pressure after authorities in China banned so-called initial coin offerings, or ICOS, after more than 2.6 billion yuan ($400 million) in new cash was raised over the first six months of the year. 

Shortly after, reports indicated that China's central bank, the People's Bank of China, was looking to ban cryptocurrency trading across all platforms, although it would allow investors to continue to swap their digital currencies in over-the-counter transactions.

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