An obscure Trump campaign adviser pleaded guilty to lying to FBI agents about contacts with people who claimed to have ties to top Russian officials, in the first criminal charges alleging links between the campaign and Moscow, said court documents released on Monday.

George Papadopoulos, who joined the Trump presidential campaign in March 2016, lied in January about communicating with those individuals to arrange a meeting between then-Republican presidential candidate Donald Trump and Russian President Vladimir Putin, Special Counsel Robert Mueller said in the documents.

The documents said an unidentified campaign official advised Papadopoulos around May 2016 that Trump himself "is not doing these trips" but that "it should be someone low-level in the campaign so as not to send any signal."