National Security Adviser Michael Flynn answers questions in the briefing room of the White House February 1, 2017 in Washington, DC.

Special counsel Robert Mueller is looking into whether or not Michael Flynn was involved in an attempt to obtain Hillary Clinton's emails from Russian hackers, The Wall Street Journal reported Friday, citing people familiar with the matter.

In June, the Journal reported that Republican operative Peter Smith had sought emails that he thought were stolen from Clinton's private server. But the newspaper noted that there is no evidence the server had been hacked.

Mueller is investigating Russian efforts to meddle in the 2016 election as well as whether there was any collusion between the Trump campaign and the Kremlin.

The Journal's Friday report said special counsel investigators have been interviewing people to determine whether Flynn, his son and his consulting firm Flynn Intel Group were involved in the effort. They are also probing Smith's relationship with many Trump campaign advisors and aides, the newspaper reported.

In attempting to recruit others to his cause, sources previously told the Journal that Smith had implied he was working with Flynn, who was then campaign advisor to Donald Trump.

Meanwhile, NBC News reported Friday that Mueller has subpoenaed public relations executives who worked with former Trump campaign chief Paul Manafort, who is another key figure in the special counsel's investigation.

Read the full report in The Wall Street Journal.