A former FBI Director has been appointed special prosecutor to take over the Justice Department's investigation into possible Russian interference in the 2016 election.
Robert Mueller will probe any potential ties Trump campaign officials may have had with Russians.
Deputy Attorney General Rod Rosenstein was charged with appointing the special prosecutor after Attorney General Jeff Sessions recused himself from the Russia probe because he had lied about meeting with Russian officials.
The decision by Mr Rosenstein follows a week of intensifying pressure on the Justice Department to make sure that its investigation into the White House is independent.
Mr Rosenstein was identified by the White House as having played an influential role in Mr Comey's firing, though Donald Trump later said that he would have fired him with or without a good reason being presented from the deputy attorney general.
"My decision is not a finding that crimes have been committed or that prosecution is warranted," Mr Rosenstein said. "I have made no such determination."
Mr Trump responded to the appointment of a special prosecutor by saying the investigation will confirm there was "no collusion" with the Kremlin.
"As I have stated many times, a thorough investigation will confirm what we already know - there was no collusion between my campaign and any foreign entity," he said in a statement released by the White House.
"I look forward to this matter concluding quickly. In the meantime, I will never stop fighting for the people and the issues that matter most to the future of our country."
Mr Trump's surprising decision last week to fire former FBI Director James Comey - and subsequent reports that the President had allegedly asked Mr Comey to stop the FBI's Russia probe - sent Washington into a frenzy and resulted in several members of Congress calling for special prosecutors to look into the matter.
Pundits on cable television hailed the special prosecutor appointment as a major development in and those who have worked with Mr Rosenstein - including former US attorney Preet Bharara, who was fired by Mr Trump - said that Mr Mueller is one of the best choices possible to run the investigation.
"Based on 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," Mr Rosenstein said.
Mr Mueller is a respected figure in American law enforcement circles. He headed the FBI from 2001 to 2013 and served under Presidents George W Bush and Barack Obama.
Mr Obama asked him to stay on at the FBI past the usual 10 year mark.
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.
As special prosecutor, Mr Mueller would still be answerable to Mr Rosenstein, who is answerable to the president, but he will have greater autonomy to run the investigation than if he were usual US attorney.
Separate investigations are ongoing in Congress.Reuse content