Special Counsel Robert Mueller informed top U.S. Justice Department officials three weeks ago that he would not be reaching a conclusion on whether President Donald Trump had obstructed justice during the probe into Russian interference in the 2016 election, a U.S. Justice official said Monday.

The decision by Mueller not to reach a determination was "unexpected," the person added, speaking anonymously in order to discuss private conversations involving U.S. Attorney General William Barr and Deputy Attorney General Rod Rosenstein, who received the news.

NBC News' Pete Williams reported similar information Monday. "So it's not that this was just sprung on the attorney general on Friday. He knew this was where it was headed. And, of course, Rosenstein had been supervising the special counsel investigation really from the beginning because of the recusal of Jeff Sessions," Williams said. "So, this was not a surprise to them is what we're hearing today."