The special counsel investigation into allegations of collusion between members of the Trump campaign and officials of the Russian government has cost US taxpayers a whopping $25 million, a statement from the US Department of Justice (DOJ) reveals.

The Special Counsel's Office Statement of Expenditures details spending by Robert Mueller's team in addition to spending by other DOJ offices in support of the probe between April 1 and September 30 of 2018.

Department of Justice The Special Counsel's Office Statement of Expenditures for the period of April 1, 2018 through September 30, 2018.

The special counsel's office directly spent $4.6 million since April, while an additional $3.9 million was spent by other DOJ offices in support of the investigation.

The latest figures bring the total up cost of the Mueller probe to $25,215,852, according to other DOJ statements of expenditures.

But the real cost of the investigation into connections between members of the Trump campaign and Russia is even greater. Mueller was appointed in May 2017 to take over an already-existing probe initiated by fired FBI agent Peter Strzok at the end of July 2016. So that's more than 10 months of expenses not accounted for in the $25 million total.

Mueller took over the probe with the mandate of investigating "(i) any links and/or coordination between the Russian government and individuals associated with the campaign of President Donald Trump; and (ii) any matters that arose or may arise directly from the investigation."

So far, Mueller has failed to secure any indictments in relation to the primary mandate of the probe.