"[Trump] is clearly upset about this, he understands the threat it poses to our national security and he’s going to make sure he continues to make sure that that stops," Spicer told reporters regarding the issue of leaks.
On Monday night, Flynn announced his decision to leave the post amid a growing controversy surrounding leaked information about his conversations with Russian Ambassador Sergey Kislyak before Trump's inauguration.
"All of this information was leaked…We have an issue where classified information of which this would be, is handled in such a way that it is being given out," Spicer added.
The White House press secretary said the amount of leaks coming out of people who are "entrusted" with US national security secrets are a "real concern for this president."
