Announcing ex-FBI chief Robert Mueller's appointment to lead the probe on Russia, US Deputy Attorney General Rod Rosenstein said "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."

In a short statement following his appointment, Mueller said he would "accept this responsibility and will discharge it to the best of my ability.”

The US Justice Department's surprise announcement on Wednesday comes as US President Donald Trump faces accusations he sought to deliberately stall an FBI investigation into links between his former National Security Advisor Michael Flynn and Russia.

US media reported earlier this week that former FBI Director James Comey described in a memo an encounter with Trump in which the president encouraged him to drop the inquiry into Flynn. The White House denied the conversation took place in the way Comey recounted in his written memo. US courts have regarded written FBI agent notes as evidence a conversation took place.

President Trump fired Comey from his job of leading the FBI last week, prompting some Democrats to raise questions about whether Trump was trying to interfere with the FBI's investigations into his team.

Comey had previously been leading the federal probe into whether Moscow coordinated with Trump's presidential campaign officials to influence the outcome of the 2016 US presidential election - the probe Mueller is set to take over, though it is unclear if Mueller's inquiry will start from scratch or work from information already collected by the FBI.

Mueller will be granted broad powers as special counsel, allowing him not only to investigate Russian interference in last year's election, but also any actions deemed pertinent to the probe - possibly including Trump's decision to fire Comey.

In an article published late Wednesday, The New York Times reported that Flynn told Trump's transition team he was under federal investigation. He was hired anyway and was later fired after serving just 24 days as national security advisor.

White House in the dark

Reports suggest the White House was given little advance notice of Mueller's appointment prior to its public announcement.

Responding to the news, Trump said that a "thorough investigation will confirm what we already know - there was no collusion between my campaign and any foreign entity." He added that he looked forward to the matter concluding "quickly."

Trump has repeatedly dismissed the FBI and congressional probes into his campaign as a "hoax," while White House Press Secretary Sean Spicer said on Monday he did not believe that a special prosecutor was needed as part of the investigation.

Bipartisan support for Mueller appointment

Since Comey's dismissal, Democrats had called for an independent figure from outside of the Justice Department to take over the investigation. Though Mueller will officially still be part of the Justice Department, Democrat lawmakers have hailed his appointment.

House Minority Leader Nancy Pelosi described Mueller as a "respected public servant of the highest integrity," adding, "A special prosecutor is the first step, but it cannot be the last. Director Mueller will still be in the chain of command under the Trump-appointed leadership of the Justice Department."

Even a number of Republican lawmakers, who have largely come out in support of Trump in the initial months of his presidency, welcomed the announcement. 

House Speaker Paul Ryan said Mueller's appointment was in line with the goal of ensuring that "thorough and independent investigations are allowed to follow the facts wherever they may lead."

Meanwhile, the Republican chairman of the House Oversight Committee, Jason Chaffetz, described Mueller as a "great selection. Impeccable credentials. Should be widely accepted."

Mueller: an asset to US security

Mueller was appointed by President George W. Bush as FBI director in 2001 and tasked with leading drug cases, white-collar felonies and violent crimes. A week later, however, the US was hit by the September 11 terror attack, effectively transforming Mueller and the FBI's mission statement. Over the next 12 years, he oversaw the bureau's move to also becoming a leading anti-terror force.

By the end of his tenure, Mueller was considered so valuable to US security that President Barack Obama urged him to stay at the helm of the FBI for two years beyond his 10-year term. In 2013, he was succeeded by James Comey.

dm/gsw (AP, Reuters)