President Donald Trump declared himself the victim of the “greatest witch hunt” in US political history as it emerged his campaign advisers had 18 contacts in seven months with Russian officials before the election.

Michael Flynn, his former national security adviser, is said to have discussed setting up a back channel for Mr Trump to communicate with Vladimir Putin once he was president.

The disclosures were made as the White House was left reeling by the appointment of an independent special counsel to investigate Russia’s role in the US election.

Mr Trump was given no advance notice of the decision by his own deputy attorney general, Rod Rosenstein, who appointed former FBI director Robert Mueller to the role.