As President Trump assumed office, a large number of top diplomats at the State Department were asked to step down, according to two insiders who spoke to CBS News.

The significant reshuffle impacted a minimum of 20 officials from the State Department, comprising both career diplomats and politically appointed leaders. These officials were informed about their dismissal as early as the preceding Friday. This included all under secretaries and assistant secretaries, even those heading regional bureaus responsible for managing U.S. foreign relations across six global regions, confirmed the sources.

The State Department has refrained from making any comments so far.

While it’s customary for incoming administrations to choose their politically appointed senior officials within the State Department, the scale and rapidity of the current leadership’s termination – including career officials – is quite surprising, the source expressed.

Traditionally, seasoned career diplomats have stayed on in senior roles while the new administration’s choices for political appointees await Senate confirmation. Now, an entire layer of leadership needs to be replaced by foreign and civil service diplomats, who may not have equivalent senior management experience, added the source.

Among those asked to step down prior to Mr. Trump’s inauguration included career diplomat John Bass, who served as the third-ranking official under Secretary of State Antony Blinken, and Geoff Pyatt, the assistant secretary for energy resources, as learned by CBS.

In his parting address at the State Department on Friday, Blinken praised Bass as the finest foreign service officer of this generation.

The Foreign Service Institute, responsible for managing foreign service careers, reported a high volume of calls on Friday as it grappled with reassignments for the affected individuals. Generally, there is a grace period of a few months during which they are reassigned to new roles.

Despite the large-scale leadership reshuffle and Mr. Trump’s regular criticism of the so-called “deep state,” the department’s staff maintain a sense of optimism about Sen. Marco Rubio, who is likely to be confirmed as the new secretary of state, insiders informed CBS News. However, there are concerns about the new leadership of the State Department and the duration of Rubio’s tenure in the top job.

Mr. Trump and Rubio share similar views on several foreign policy matters, including the need for a tougher stance on China and Iran, endorsing the recent ceasefire deal between Israel and Hamas, and advocating for a political resolution between Russia and Ukraine to end the ongoing conflict.

The Trump White House announced on Monday that career ambassador Lisa Kenna will serve as the acting secretary of state until Rubio is confirmed.

Reuters was the first to report the commencement of the reshuffle last week, when three senior career diplomats in charge of the department’s workforce and internal coordination were asked to step down.

Editor’s note: Contrary to an earlier version of this report, Bridget Brink, the U.S. ambassador to Ukraine, was not asked to resign immediately.