The operators of two exchanges for the virtual currency Bitcoin have been arrested in the US.

The Department of Justice said Robert Faiella - known as "BTCKing" - and Charlie Shrem from BitInstant have both been charged with money laundering.

The authorities said the pair were engaged in a scheme to sell more than $1m (£603,000) in bitcoins to users of online drug marketplace the Silk Road.

The site was shut down last year and its alleged owner was arrested.