Donald Trump has attacked the appointment of a former FBI director to investigate alleged ties between his campaign team and Russia.
"With all of the illegal acts that took place in the Clinton campaign & Obama Administration, there was never a special councel [sic] appointed!" the President wrote on Twitter.
"This is the single greatest witch hunt of a politician in American history!"
Mr Trump did not elaborate on the "illegal acts", but appeared to be referring to the closed investigation into Hillary Clinton's use of a private email server for government communications, including classified information.
He was reacting to the Justice Department's appointment of James Comey's predecessor, Robert Mueller, as a special counsel to lead the federal investigation into claims the Trump campaign collaborated with Moscow to sway the 2016 election.
Mr Mueller, whose arrival came as a surprise following months of calls for an outside prosecutor, will have sweeping powers and the authority to prosecute any crimes he uncovers.
His broad mandate gives him not only oversight of the Russia probe, but also “any matters that arose or may arise directly from the investigation" - potentially including the removal of Mr Comey.
Mr Mueller, a former federal prosecutor who took up his FBI days before 9/11, is highly valued by Republicans and Democrats and was asked to extend his term by Barack Obama.
Attorney General Rod Rosenstein said the appointment was “necessary in order for the American people to have full confidence in the outcome”.
The Justice Department's move has escalated the legal stakes and potential damage for Mr Trump, who has repeatedly dismissed the scandal as "fake news" and a "hoax".
In a written statement, Mr Trump insisted again that there were no ties between his campaign and Russia.
“A thorough investigation will confirm what we already know — there was no collusion between my campaign and any foreign entity,” he said. “I look forward to this matter concluding quickly.”
His White House has been embroiled in a series of controversies that escalated last week with the dismissal of Mr Comey, who was previously leading the Russia investigation as head of the FBI.
The biggest names involved in the Trump-Russia investigation
The biggest names involved in the Trump-Russia investigation
1/11 Paul Manafort
Mr Manafort is a Republican strategist and former Trump campaign manager. He resigned from that post over questions about his extensive lobbying overseas, including in Ukraine where he represented pro-Russian interests.
2/11 Mike Flynn
Mr Flynn was named as Trump's national security adviser but was forced to resign from his post for inappropriate communication with Russian Ambassador to the US Sergey Kislyak. He had misrepresented a conversation he had with Mr Kislyak to Vice President Mike Pence, telling him wrongly that he had not discussed sanctions with the Russian.
3/11 Sergey Kislyak
Mr Kislyak, the Russian ambassador to the US, is at the centre of the web said to connect President Donald Trump's campaign with Russia.
4/11 Roger Stone
Mr Stone is a former Trump adviser who worked on the political campaigns of Richard Nixon, George HW Bush, and Ronald Reagan. Mr Stone claimed repeatedly in the final months of the campaign that he had backchannel communications with WikiLeaks founder Julian Assange and that he knew the group was going to dump damaging documents to the campaign of Democratic candidate Hillary Clinton - which did happen. Mr Stone also had contacts with the hacker Guccier 2.0 on Twitter, who claimed to have hacked the DNC and is linked to Russian intelligence services.
5/11 Jeff Sessions
The US attorney general was forced to recuse himself from the Trump-Russia investigation after it was learned that he had lied about meeting with Russian Ambassador to the US Sergey Kislyak.
6/11 Carter Page
Mr Page is a former advisor to the Trump campaign and has a background working as an investment banker at Merrill Lynch. Mr Page met with Russian Ambassador to the US Sergey Kislyak during the 2016 Republican National Convention in Cleveland. Mr Page had invested in oil companies connected to Russia and had admitted that US Russia sanctions had hurt his bottom line.
7/11 Jeffrey "JD" Gorden
Mr Gordon met with Russian Ambassador to the US Sergey Kislyak during the 2016 Republian National Convention to discuss how the US and Russia could work together to combat Islamist extremism should then-Republican presidential candidate Donald Trump win the election. The meeting came days before a massive leak of DNC emails that has been connected to Russia.
8/11 Jared Kushner
Mr Kushner is President Donald Trump's son-in-law and a key adviser to the White House. He met with a Russian banker appointed by Russian President Vladimir Putin in December. Mr Kushner has said he did so in his role as an adviser to Mr Trump while the bank says he did so as a private developer. Mr Kushner has also volunteered to testify in the Senate about his role helping to arrange meetings between Trump advisers and Russian Ambassador to the US Sergey Kislyak.
9/11 James Comey
Mr Comey was fired from his post as head of the FBI by President Donald Trump. The timing of Mr Comey's firing raised questions around whether or not the FBI's investigation into the Trump campaign may have played a role in the decision.
10/11 Preet Bharara
Mr Bahara refused, alongside 46 other US district attorney's across the country, to resign once President Donald Trump took office after previous assurances from Mr Trump that he would keep his job. Mr Bahara had been heading up several investigations including one into one of President Donald Trump's favorite cable television channels Fox News. Several investigations would lead back to that district, too, including those into Mr Trump's campaign ties to Russia, and Mr Trump's assertion that Trump Tower was wiretapped on orders from his predecessor.
11/11 Sally Yates
Ms Yates, a former Deputy Attorney General, was running the Justice Department while President Donald Trump's pick for attorney general awaited confirmation. Ms Yates was later fired by Mr Trump from her temporary post over her refusal to implement Mr Trump's first travel ban. She had also warned the White House about potential ties former National Security Adviser Michael Flynn to Russia after discovering those ties during the FBI's investigation into the Trump campaign's connections to Russia.
A leaked memo written by Mr Comey generated further alarm after claiming the President asked him to end a probe into ex-national security advisor Michael Flynn.
His removal came shortly before Mr Trump met Russian foreign minister Sergey Lavrov and ambassador Sergey Kislyak - whose discussions with Mr Flynn resulted in the latter being fired.
Reports denied by the White House claim the President disclosed classified information from a foreign intelligence partner on Isis during the closed-door meeting.
Vladimir Putin dismissed the claims, saying he had a transcript that disproved the allegations amid concern international cooperation could be damaged.
Mr Trump has repeatedly attacked ongoing FBI and congressional investigations and blamed "leakers" inside US intelligence agencies for sabotaging him.
Addressing the US Coast Guard Academy on Wednesday, he claimed: “No politician in history, and I say this with great surety, has been treated worse or more unfairly.
"You can't let the critics and the naysayers get in the way of your dreams...the more righteous your fight, the more opposition that you will face.”
Additional reporting by APReuse content