Lt. Gen. H.R. McMaster said Tuesday that members of the President Trump's National Security Council should understand it is treasonous to leak to the media about national security deliberations.

Such leaks, an unwelcome fixture in Trump's White House often derided by the president, have become a real challenge in recent years as the NSC has grown to its current size of about 367 members and the administration has taken steps to trim the size of the council, said McMaster, who is the president's national security adviser.

The general, who spoke at the Center for Strategic and International Studies think tank, said the "real dilemma" for the NSC and its size is that more personnel can add expertise and different perspectives to solving security and foreign policy concerns.

"But in recent years, in particular, the problem with leaks has become a real challenge to national security and so I think what is very important is that everyone who is involved in these sort of policy discussions understand the sacred trust that is placed in them, and they realize that speaking to the media about government deliberations is treasonous when it involves national security," McMaster said.

The NSC was at its largest -- 400 personnel -- under the Obama administration when it was often criticized for micromanaging the military, and McMaster said he has cut about 40 personnel, though only about 160 current council staff work directly on policy.

"We have made a conscious effort to reduce the size of the staff and to make sure that form follows function," he said. "Does that mean we can't get smaller? No, we can, I think … [but] I think we are at a good place now in terms of the size and effectiveness."

McMaster said the NSC had also overstepped its responsibilities as it grew and under Trump's guidance it has ceded day-to-day operations back to the heads of agencies, especially Secretary of State Rex Tillerson, to help come up with policies.

Meanwhile, the NSC is more focused on long-term strategic planning, he said.

"Many of you watched us do it on the Cuba policy, which was probably the most public one," McMaster said. "But there are signed policies on Iran, for example, which you will hear about more this week."