President Donald Trump on Wednesday responded to the appointment of a special counsel to investigate his campaign’s ties with Russia by protesting his innocence and calling for the probe to conclude “quickly.”

“A thorough investigation will confirm what we already know — there was no collusion between my campaign and any foreign entity,” Trump said in a tersely written statement.

“I look forward to this matter concluding quickly,” Trump said, without directly commenting on the Justice Department’s appointment of former head of the FBI Robert Mueller as a special investigator.

The US Department of Justice Wednesday named Mueller as special counsel to lead the investigation into Russian meddling in the 2016 election, and possible collusion with Donald Trump’s team.

The US president stands accused of seeking to stall the politically-explosive probe following his shock dismissal of the FBI chief James Comey, and allegations that he asked Comey to drop his investigation of a former aide.

Deputy Attorney General Rod Rosenstein tapped Mueller — a widely-respected figure who headed the FBI for the decade after the 9/11 attacks — to take over the FBI’s probe of “Russian government efforts to influence the 2016 presidential election and related matters.”

“Based upon the unique circumstances, the public interest requires me to place this investigation under the authority of a person who exercises a degree of independence from the normal chain of command,” Rosenstein said in a statement.

In this June 19, 2013, file photo, former FBI Director Robert Mueller testifies on Capitol Hill in Washington. (AP Photo/J. Scott Applewhite, File)

In this June 19, 2013, file photo, former FBI Director Robert Mueller testifies on Capitol Hill in Washington. (AP Photo/J. Scott Applewhite, File)

In a short statement, Mueller said “I accept this responsibility and will discharge it to the best of my ability.”

His law firm, WilmerHale, says he resigned immediately upon his Wednesday appointment by the Justice Department. Spokespeople declined to comment further.

Capping days of political drama in Washington, the appointment came as pressure mounted in Congress for an independent probe into ties between Trump’s campaign and Moscow, which US intelligence chiefs say interfered to tilt the election in the Republican’s favor.

A special counsel is empowered to conduct the investigation independent of the Justice Department hierarchy, with a dedicated staff of his choosing. The counsel is not required to consult with or keep informed the attorney general or deputy attorney generals on the course of the probe.

The special counsel is also authorized to prosecute any crimes unearthed by the investigation.

Rosenstein’s order came a week after he played a key role in Trump’s firing of Comey, who had overseen the FBI investigation into Russia’s election interference since last July.

This file photo taken on March 20, 2017 shows FBI Director James Comey  during the House Permanent Select Committee on Intelligence hearing on Russian actions during the 2016 election campaign on Capitol Hill in Washington, DC. (AFP PHOTO / Nicholas Kamm)

This file photo taken on March 20, 2017 shows FBI Director James Comey during the House Permanent Select Committee on Intelligence hearing on Russian actions during the 2016 election campaign on Capitol Hill in Washington, DC. (AFP PHOTO / Nicholas Kamm)

The deputy attorney general penned a letter criticizing Comey’s handling of the probe into Hillary Clinton’s emails, which provided the White House with the rationale for firing Comey — and raised questions about Rosenstein’s own ability to remain politically independent.

His boss, Attorney General Jeff Sessions, was forced to recuse himself from the investigation in March due to his own undisclosed contacts with the Russian ambassador, Sergey Kislyak.

Pressure to place the Russia probe in independent hands intensified this week following reports that Trump pressured Comey to reel back the Russia investigation as it pertained to Michael Flynn, the national security advisor who was fired over concerns about his Russian contacts.

Trump’s alleged pressure on Comey — denied by the White House — has exposed the president to accusations of obstructing justice.

Mueller was director of the FBI from 2001 to 2013, a period when he was forced to shake up a huge bureaucracy blamed for missing evidence that could have prevented the September 11, 2001 attacks.

During his tenure he served both Republican and Democratic presidents, and is highly respected by both parties.

He is empowered to examine “any links and/or coordination between the Russian government and individuals associated with the campaign of President Donald Trump,” Rosenstein’s order says.

Trump has consistently rejected any suggestion of collusion between his camp and Moscow as “fake news” and complained in a speech on Wednesday that he had been treated “more unfairly” than any US leader in history during his fledgling presidency.

The Associated Press contributed to this report.