BILLINGS — Sixteen senior employees at the U.S. Department of Interior reassigned to new duties under the Trump administration viewed their moves as political retribution or punishment for their work on climate change, energy or conservation, according to the results of an internal investigation released Wednesday.

However, investigators said they were unable to determine if anything illegal occurred because the agency leaders did not document their rationale for the reassignments.

The findings by the Office of Inspector General follow a backlash over new jobs given to almost three dozen senior employees in the months after Trump appointee Interior Secretary Ryan Zinke took office.

Critics charged that the personnel changes were an attempt to squelch dissenting voices within an administration that has promoted energy development and downplayed climate change.

The inspector general’s report concluded the moves were made without any clear criteria and without consulting the affected employees or their supervisors.

Zinke spokeswoman Heather Swift said agency officials had acted within their legal authority when making reassignments.

She added that Interior already has adopted some of the inspector general’s recommendations aimed at increasing transparency and shielding the process from political interference. That included adding two non-political senior employees to a panel that decides on reassignments, the Executive Resources Board.

Swift did not directly address the contention that many of the reassignments were politically motivated.

Climate scientist Joel Clement, who resigned from the Interior Department and filed a whistleblower complaint following his reassignment to an accounting office, said the report “sends up a red flag” that Congress should conduct a more thorough investigation. He also called on Zinke to resign.

“I am stunned at the level of incompetence that this report describes,” Clement said in a statement released by his attorney. “There are important reasons to keep the civil service partitioned from the political winds and whims of each new administration.”

The inspector general’s investigation included interviews with 31 of the 35 senior employees who faced reassignment under Zinke. Only eight of those employees viewed their moves positively. Four had a neutral opinion.

Interior Deputy Secretary David Bernhardt appeared to deflect some of the blame for how the reassignments were handled, in a March 30 letter to the Inspector General’s Office released Wednesday.

Guidelines for the government’s Executive Resources Boards had been developed in 2009, during the administration of President Barak Obama, but were never acted upon at Interior until after Trump took office, Bernhardt wrote. He also said that delays in Senate confirmation of key leadership positions had resulted in fewer people capable of driving improvements.

Bernhardt said the Interior Department would “continue to use (senior personnel) reassignments robustly as a management tool.”