A former US undercover agent involved in an investigation into the dark web marketplace Silk Road has admitted a series of crimes.

Carl Force, 46, faces up to 20 years in prison after pleading guilty to charges of extortion, money-laundering and obstruction of justice.

He stole more than $700,000 (£448,000) in the digital currency Bitcoin.

Force also secretly solicited payment from the marketplace's operator for information about the US investigation.

During the course of the investigation, the former US Drug Enforcement Administration (DEA) agent posed as a drug dealer with connections to hit-men using the alias Nob.

He was given the task of communicating with Ross Ulbricht, the man who was subsequently jailed for life for running Silk Road, prosecutors said.