U.S. President Donald Trump on Wednesday called on Attorney General Jeff Sessions to end a federal investigation into Russian interference in the 2016 presidential election and whether there was any cooperation by his campaign with Moscow.

The Republican president has long complained about the criminal probe into his White House victory but Wednesday's comment appeared to be his most direct call for shutting down special counsel Robert Mueller's investigation.

In a series of tweets, Trump called it a "TOTAL HOAX" the idea his campaign worked with Moscow. "This is a terrible situation and Attorney General Jeff Sessions should stop this Rigged Witch Hunt right now, before it continues to stain our country any further," he said.