The State Department's internal watchdog has concluded there was an "appearance of undue influence or favoritism" but no actual wrongdoing in the way several high-profile investigations of alleged misconduct by U.S. diplomats were handled.

In a report released Thursday, the department's inspector general said it had found such appearances in three of eight cases it had looked at, including one involving a U.S. ambassador in Europe alleged to have solicited prostitutes in a park. That investigation was halted before any evidence was found to support or dispute the allegations after the diplomat was summoned to Washington and denied the charges.

The report said no appearance of impropriety was found in four of the cases and a review of the eighth case remains open.

Although it found no evidence of wrongdoing, the inspector general said the appearance of favoritism is "problematic because it risks undermining confidence in the integrity of the department and its leaders." It recommended that the department revise its approach to alleged misconduct by applying established procedures consistently regardless of the allegation or who is being investigation.

It said it stood by an earlier determination that the Bureau of Diplomatic Security's Special Investigations Division, which looks into allegations of substance abuse, domestic violence, firearms violations, sex crimes and other serious misconduct, suffers from at least the perception of a lack of independence.

That report said the division "lacks a firewall to preclude ... hierarchies from exercising undue influence in particular cases."

The potential issues came to light last year in June after at least one investigator complained that probes into the eight cases had been quashed by higher-ups for political or other reasons.