The vice chairman of the Bitcoin Foundation, a trade group promoting the adoption of the digital currency, has been charged by US prosecutors with conspiring to commit money laundering by helping to funnel cash to illicit online drugs bazaar Silk Road.

Charlie Shrem, who had financial backing from the Winklevoss twins and is well known as one of the bitcoin's biggest global promoters, was arrested on Sunday at John F Kennedy International Airport in New York, the US Attorney's Office in Manhattan said.

Shrem, who was also charged with operating an unlicensed money transmitting business, appeared in US District Court in Manhattan on Monday and was released on $1 million bond.

"At this point the allegations in the complaint are simply allegations, and Mr Shrem is presumed innocent," his lawyer Keith Miller said.

The 24-year-old entrepreneur, who lives above a bar he jointly owns in Manhattan that accepts bitcoins as payment, was CEO of BitInstant, a bitcoin exchange company that closed last summer. According to prosecutors, Shrem conspired with a Florida resident, Robert Faiella, who ran an illegal exchange, to sell more than $1 million in bitcoins to users of Silk Road, which was shuttered by authorities last year.

Faiella, 52, is also charged in the complaint filed in US District Court in Manhattan with conspiring to commit money laundering and operating an unlicensed money transmitting business. He was arrested at his home in Coral Gables, Florida. At his court hearing on Monday in federal court in Florida, Faiella consented to detention until Wednesday, at which point there will be a bail hearing.

Shrem could not be reached for comment. A person who answered the phone at Faiella's house and declined to be identified said, "Nobody wants to talk."

Bitcoin is a digital currency that is not backed by a government or central bank and whose value fluctuates according to demand by users. Users can transfer bitcoins to each other over the Internet and store the currency in digital "wallets."

The criminal complaint says that Shrem, in addition to knowing that Faiella's business was funneling money into Silk Road, also used Silk Road himself to buy drugs, including marijuana-infused brownies.

"When Bitcoins, like any traditional currency, are laundered and used to fuel criminal activity, law enforcement has no choice but to act," Preet Bharara, the US attorney for Manhattan, said in a statement emailed to the press on Monday. "We will aggressively pursue those who would co-opt new forms of currency for illicit purposes."

Bharara has said recently that prosecutors are not going after Bitcoin itself and view it as they view any other currency in which transactions are sometimes made illegally.

US law enforcement officials have vowed to pursue any criminal activity in the nascent Bitcoin world as regulators try to formulate their approach to the digital currency.

The charging of a prominent Bitcoin Foundation official may be a blow to Bitcoin's prospects, though it did not have a huge immediate impact on trading. Bitcoins were exchanging hands at $970 late on Monday, down from prices above $1,000 earlier this month but up from around $150 four months ago on the Tokyo-based exchange MtGox.

Winklevoss Capital, which is run by twin brothers Cameron and Tyler Winklevoss, invested in BitInstant in 2012 and led a capital-raising effort last May that raised $1.5 million. The twins, who are best known for their failed lawsuit against Facebook founder Mark Zuckerberg in which they had claimed he had stolen their idea for an online social networking platform at Harvard, have been seeking regulatory approval for a bitcoin exchange-traded fund.

"When we invested in BitInstant in the fall of 2012, its management made a commitment to us that they would abide by all applicable laws - including money laundering laws - and we expected nothing less," the Winkelvoss twins said in a statement.

"Although BitInstant is not named in today's indictment of Charlie Shrem, we are obviously deeply concerned about his arrest," they said. "We were passive investors in BitInstant and will do everything we can to help law enforcement officials." - Reuters