Echoing the language of his accusers and critics, U.S. President Donald Trump alleged on Twitter that special counsel Robert Mueller's investigative team is "MEDDLING" in the upcoming midterm elections and blamed Democrats for "Collusion."

His statement came as Mueller investigates allegations of Russian meddling in the 2016 presidential election and whether any Trump campaign aides colluded with the Kremlin to tip the outcome in the Republican candidate's favour.

So far, four Trump associates have been charged in Mueller's investigation, and three have pleaded guilty.

Trump has repeatedly referred to Mueller's team as "13 angry Democrats," although Mueller is a Republican who was appointed by Trump's deputy attorney general, Rod Rosenstein, and before that was named FBI director in 2001 by Republican President George W. Bush.

The tweet appeared to be a reference to the fact that multiple lawyers on Mueller's team, before signing up for the assignment, contributed money to Democratic candidates, including Clinton. The Justice Department is barred from discriminating against employees or applicants on the basis of political affiliation.

Later Tuesday morning, Trump appeared to be taking guidance from some of his advisers and supporters to heart, saying he needed to focus more of his attention on issues important to Americans and less on the Russia investigation.