WASHINGTON (AFP) - The US Justice Department said Tuesday (Dec 1) it had named an independent special counsel to continue probing the 2016-2018 investigations of possible collusion between Russia and President Donald Trump's campaign.

Attorney-General William Barr appointed federal prosecutor John Durham to investigate the Russia investigators, which could include the former FBI director James Comey and previous special counsel Robert Mueller.

While Mr Durham has already been examining those matters under Mr Barr, making him a special counsel will allow Mr Durham to continue unimpeded under a new attorney-general after Mr Trump steps down on Jan 20 and Democrat Joe Biden assumes the presidency.

Mr Barr made the appointment on Oct 19, but apparently held off on announcing it to avoid impacting the looming presidential election, in which Mr Biden defeated Mr Trump.

While Mr Biden is expected to name his own attorney-general, Mr Barr's replacement will find it politically difficult to force the end of Mr Durham's special counsel operation.

Mr Barr chose Mr Durham in April 2019 to investigate allegations, made most prominently by Mr Trump, that the Russia investigation was corrupt and a political "witch hunt" by the "deep state" aimed at undermining his administration.

So far Mr Durham has only made one case, against an FBI lawyer who had altered an email in documents filed to obtain wiretap permission against a Trump campaign aide.

Meanwhile the Justice Department's own inspector-general, who likewise reviewed the handling of the Russia investigations, found no significant wrongdoing.

But in his Oct 19 order, Mr Barr said Mr Durham's ongoing probe has "developed into a criminal investigation, which remains ongoing."

Mr Durham's focus, according to Mr Barr's order, will remain the FBI's "Crossfire Hurricane" investigation launched in July 2016, and Mr Muller's investigation initiated in May 2017.

Both honed in on Russian hacking and social media manipulation in favour of Mr Trump in 2016, and multiple contacts between the Trump campaign and Moscow.

The Mueller probe expanded that to cover alleged acts of obstruction by Mr Trump. In the end Mr Mueller gained convictions of six members of the Trump campaign, and issued indictments of 25 Russians.

But Mr Mueller found no evidence of criminal cooperation with Russia by the campaign, and his evidence of alleged obstruction by Mr Trump was rejected by Mr Barr.

Mr Barr's order gave Mr Durham wide latitude, however, to "investigate whether any federal official, employee, or any other person or entity violated the law in connection with the intelligence, counter-intelligence, or law-enforcement activities directed at the 2016 presidential campaigns."

According to reports Mr Durham has extended his mandate to probe issues related to Mrs Hillary Clinton, Mr Trump's Democratic opponent in the 2016 presidential race.