Robert Mueller, the special counsel overseeing the probe into Russia's interference in the 2016 U.S. election, has impaneled a grand jury, according to a report published by the Wall Street Journal Thursday.

The decision marks a turning point in the investigation. The WSJ called the grand jury a "sign that [Mueller's] inquiry is growing in intensity and entering a new phase," citing "people familiar with the matter."

A grand jury has the power to seek information related to the investigation, such as documents and witness testimony and can, with enough evidence, issue indictments

Though the grand jury does not necessarily mean Mueller intends to bring charges, it indicates he is taking the investigation seriously and may want to issue subpoenas or gather witness testimony, the WSJ said.

President Trump has vehemently denied allegations of collusion between his campaign and Russia, calling the investigation a "witch hunt."