Washington: A handful of new federal prosecutors have joined one of special counsel Robert Mueller III's cases - an indication that he is preparing to hand off at least one prosecution to others when his office completes its investigation into Russian interference in the 2016 election.

Mueller's team is asking a US federal judge to set a sentencing date for former Trump campaign adviser George Papadopoulos.

Special counsel Robert Mueller Credit:AP

In a pair of court filings on Friday, the special counsel added four assistant US attorneys to the case against Russian entities and people accused of running an online influence operation targeting American voters.

People familiar with the staffing decision said the new prosecutors are not joining Mueller's team, but rather are being added to the case so that they could someday take responsibility for it when the special counsel ceases operation.