Trump campaign had 18 undisclosed Russia contacts - Reuters

US President Donald Trump and his campaign had as many as 18 undisclosed contacts with Russian officials during last year's election, Reuters has reported.

According to sources cited by the news organisation, former national security adviser Michael Flynn and other advisers had received and made a number of undisclosed calls and emails during the final months of the race, where Trump defeated Democrat candidate Hillary Clinton.

Phone calls between Flynn and Russian ambassador Sergei Kislyak are at the centre of the reports, with an acceleration of contacts after the vote as the two allegedly sought to establish a back channel for Trump and opposite number Vladimir Putin.

There were calls for Trump to be impeached on Wednesday after a recent series of allegations surrounding his campaign links with the Kremlin. These include the sacking of FBI chief James Comey and the release of a memo from the intelligence official suggesting Trump tried to have the investigation into the links shut down.