They announced the seizure Thursday, a day after a Manhattan judge approved the seizure of the bitcoins and the website.
The seizure came three months after San Francisco entrepreneur Ross Ulbricht was arrested on charges he operated an online marketplace for illegal drugs following a crackdown on the website.
U.S. Attorney Preet Bharara (buh-RAH'-ruh) said the bitcoins were seized because they were the proceeds of crimes. The prosecutor says investigators also seized more than $130 million worth of bitcoins from computer hardware belonging to Ulbricht, but he's challenging those government forfeiture claims.
A lawyer for Ulbricht did not immediately respond to a message for comment Thursday.