Story highlights The move sent shock waves through the agency and has left career officials on edge

Two dozen career foreign and civil service officers are scrambling for reassignments

Washington (CNN) Secretary of State Rex Tillerson has reassigned a majority of the staff meant to work most closely with the top US diplomat in what career officials at the State Department fear is the start of a major reorganization.

The news sent shock waves through the agency and has left career officials on edge, in part because of its abrupt nature -- taking place before their assignments end this summer and replacements have been found -- and in part because these officials help the secretary, a government novice, work with policy experts throughout the building.

While Tillerson was on his first overseas trip at the G20 in Bonn, Germany, his aides told the entire staff in the offices of the deputy secretary of state for management and resources and the State Department counselor that their current assignments were prematurely coming to an end, according to senior aides.

Staff who worked for the head of the latter division, State Department Counselor Kristie Kenney, was told Tillerson does not intend to keep her position. Kenney was one of the last remaining senior officials at the department, having served as an ambassador under Presidents Bill Clinton, George W. Bush and Barack Obama, and is expected to retire next week. An aide to Tillerson told CNN, "no decisions have been made" about scrapping the offices permanently.

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Altogether, the move left some two dozen career foreign and civil service officers scrambling for reassignments within the department.

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