-- The United States Department of Justice has announced that a special counsel has been appointed to investigate Russian interference into last year's presidential election and links or coordination with the campaign of President Donald Trump.
In a statement, Rosenstein said, "My decision is not a finding that crimes have been committed or that any prosecution is warranted. I have made no such determination. What I have determined is that 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."
"I accept this responsibility and will discharge it to the best of my ability," said Mueller in a statement.
Mueller will have 60 days to put together a budget for resources to conduct the investigation and that budget must be approved by Rosenstein. Attorney General Jeff Sessions previously recused himself from all matters related to the presidential campaign.
"Special Counsel Mueller will have all appropriate resources to conduct a thorough and complete investigation, and I am confident that he will follow the facts, apply the law and reach a just result," said Rosenstein in the statement.
Justice Department officials were in touch with Mueller within days of the firing of FBI Director James Comey last week. Comey confirmed in March that the bureau was actively investigating Russian influence and collusion with the Trump campaign.
As special counsel, Mueller can be expected to have the full powers and independent authority to exercise all investigative and prosecutorial functions of any United States attorney. These powers include the ability to take matters before a grand jury, issue subpoenas and assign federal agents to the case.
The White House was informed of the decision less than an hour before it was publicly announced Wednesday and released a statement from the president over two hours later.
"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," read the statement from Trump. "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."
Administration officials have previously said that they see no need for a special counsel. On Monday, White House press secretary Sean Spicer said the investigations led by committees in the House and Senate, plus the FBI, were sufficient.
"I don’t know why you need additional resources when you already have three entities," said Spicer.
Mueller, 72, served as FBI director for 12 years after his nomination by President George W. Bush in 2001. Prior to leading the bureau, Mueller was the U.S. attorney for the Northern District of California and served as an assistant attorney general in between stints in private practice. He joined law firm WilmerHale as a partner in 2014 but resigned "immediately upon his appointment" Wednesday, according to a firm spokesperson.
The appointment of Mueller as special counsel comes amid a fraught week for the Trump administration. On Tuesday, ABC News learned from sources that Comey, Mueller's successor at the FBI, was asked by Trump in February to end the bureau's investigation into former national security adviser Michael Flynn. Comey then wrote of the request in a memo he shared with top FBI associates.
Flynn was fired after it was revealed that he misled administration officials, including Vice President Mike Pence, about the nature of his conversations with Russian officials, including Russia's Ambassador to the U.S. Sergey Kislyak, prior to Trump's inauguration.
On Monday, it was uncovered that Trump shared classified intelligence with Russian officials, one of whom was Kislyak, during a meeting at the White House last week. The president later said he had the "absolute right" to disclose the information, even as members of his administration disputed the story.
ABC News' Jack Date contributed to this report.