Muller says “Charging Trump was not an option”

US Special Counsel Robert Mueller has said charging President Donald Trump with a crime was not an option, in his first comments on the Russia inquiry.

He reiterated that his report did not exonerate the president and that legal guidelines prevent the indictment of a sitting president.

Mueller did not rule out testifying in Congress but said he would not give information that was not in his report.

He also said his two-year investigation did not clear Trump of improper behaviour and, while he did not use the word “impeachment,” he pointed out there were other ways to hold presidents accountable.

“The Constitution requires a process other than the criminal justice system to formally accuse a sitting president of wrongdoing,” Mueller said as he announced his resignation from the Justice Department. Reacting to the remarks, Trump said: "The case is closed! Thank you."

As special counsel, Mueller was tasked with investigating Russian interference in the 2016 presidential election.

His 448-page report said it had not established that the Trump campaign criminally conspired with Russia to influence the election. However, it did detail 10 instances where Trump had possibly attempted to impede the investigation.

His statement largely reaffirmed what was in the report released with redactions last month. He said if his team had had confidence that Trump "clearly did not commit a crime, we would have said so".

With Democratic lawmakers seeking to have him testify in Congress, Mueller said: "The report is my testimony." He also announced the formal closure of the special counsel office and his resignation from the justice department to return to private life.