Special Counsel Robert Mueller is reaching out to the Justice Department for resources, including FBI agents, as he continues to expand his investigation into claims of Russian interference in the 2016 election, according to a Bloomberg report.

The investigation has produced a number of indictments and several guilty pleas, although they are not connected to election interference. The probe has released no evidence of Trump campaign collusion with the Russian government and is under increasing pressure to conclude.

"Finish it the hell up," Rep. Trey Gowdy, R-S.C., told Deputy Attorney General Rod Rosenstein and FBI Director Christopher A. Wray last week.

Video of Gowdy:

President Trump has repeatedly called Mueller's probe a "witch hunt," pointing out 13 of the 17 members of his team are registered Democrats, and FBI agent Peter Strzok was removed from the probe after the discovery of anti-Trump text messages. On Thursday, the Associated Press reported ethical questions were being raised after an FBI agent said he was able to "shape" the investigation against Trump by revealing information to investigators.

Bloomberg reported Monday that Mueller is "making more use of career prosecutors from the offices of U.S. attorneys and from Justice Department headquarters, as well as FBI agents," calling it a sign that he might want to hand off parts of his investigation.

Mueller also is facing headwinds because of court challenges, Bloomberg said.

"According to his most recent statement of expenditures, more money is being spent on work done by permanent Department of Justice units than on Mueller's own dedicated operation. The DOJ units spent $9 million from the investigation's start in May 2017 through March of this year, compared with $7.7 million spent by Mueller's team," the report said.

The foundation of the investigation itself also has been challenged, since it likely was prompted at least in part by the so-called "dossier," a list of unverified claims about Trump compiled by a contractor with Russian ties working for a company funded by Clinton's campaign.

Despite its dubious claims, the Justice Department and the FBI submitted the dossier as evidence to obtain a warrant to spy on a Trump campaign adviser.

Rosenstein commissioned Mueller to investigate whether Trump or his associates in the campaign colluded with Russia.

But Mueller's assignments now, Bloomberg reported, have been handed over to investigators in New York, Virginia, Pittsburgh and "elsewhere."

Gowdy's demand to "finish" came during a hearing before the House Judiciary Committee last Thursday.

Rosenstein and Wray were there to explain why documents requested by Congress, which has oversight over the agencies, were being withheld.

Gowdy noted the FBI chose Strzok, whose intent to "stop" Trump from being elected was documented in a text message, to lead the Russia investigation.

The South Carolina lawmaker sarcastically described Strzok as "dispassionate and fair" while Strzok was lashing out against Trump as "destabilizing for the country" and "a disaster."