Special Counsel Robert Mueller impanels grand jury in Russia probe

Special Counsel Robert Mueller has impaneled a grand jury to investigate Russia's meddling in the 2016 election, The Wall Street Journal reported Thursday.

The move is seen as a sign the investigation into the Trump campaign is heating up and entering a new phase.

Russia has denied having a hand in the U.S. presidential election. President Trump, too, has strongly denied allegations of collusion and has frequently called the investigation a "witch hunt."

Grand juries are powerful tools that allow prosecutors to subpoena documents and get witness testimony on the record.