Washington (CNN) National security adviser Robert O'Brien is expected to make major cuts to the National Security Council staff as early as next week, two sources familiar with the matter told CNN.

Some people with knowledge of the impending change previously said once President Donald Trump's impeachment trial had concluded, O'Brien was expected to oust about a dozen or so officials as part of an effort to streamline the NSC, which critics charge has become too large.

O'Brien has largely been downsizing the NSC by attrition and getting staffers detailed to the council from other departments to return earlier than planned to their home agencies, but one of the sources told CNN it looks like the final phase will involve more direct firings and cuts.

"So it's bloated. We're going to bring it back to a size that's manageable and efficient. And look, the folks who are there, they really need to want to serve the President," O'Brien told Fox News' Laura Ingraham Tuesday night.

"What I said when I came to the NSC is that I would drastically downsize it," he added.

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