The State Department's internal watchdog has asked outside law enforcement experts to review how complaints of serious misconduct or crimes against American diplomats are investigated, amid charges that some probes have been improperly halted by senior officials.

The department said Tuesday the assessment was contracted by the Office of the Inspector General to determine if investigators in the Bureau of Diplomatic Security have the independence necessary to do their jobs effectively. Officials said the review is expected to be complete later this summer.

The review was ordered after at least one investigator told the inspector general that probes into several cases, including allegations of diplomats soliciting prostitutes, had been quashed by higher-ups for political or other reasons.

The State Department adamantly denied that any allegations of questionable or illegal behavior by diplomats have been covered up and said that any proven wrongdoing is punished administratively or prosecuted criminally.

"We hold all employees to the highest standards," spokeswoman Jen Psaki said after CBS News on Monday reported details of an internal department memo listing eight cases in which probes allegedly had been improperly curtailed.

"We take allegations of misconduct seriously and we investigate thoroughly. All cases mentioned in the CBS report were thoroughly investigated or (are) under investigation. And the department continues to take action," she said.

The New York Post on Tuesday reported more details of the allegations, including claims that an ambassador currently serving in Europe had routinely ditched his security guards to solicit prostitutes in a park. The ambassador in question has denied any impropriety.

The State Department declined to comment on any specific cases, citing privacy considerations involving personnel records.

But Psaki maintained that all misconduct charges are fully investigated and that proven wrongdoing is dealt with either through the department's internal administrative process or prosecuted if it involves criminal activity.

"The notion that we would not vigorously pursue criminal misconduct in any case is preposterous," she said.

The outside review of the investigative process was ordered after a February report from the inspector general found that that 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.

The 36-page report, released on March 15, well before the news reports about specific instances of alleged misbehavior surfaced, did not find any instances of improper interference in investigations but said the division "lacks a firewall to preclude ... hierarchies from exercising undue influence in particular cases."

It noted that independence in both "fact and appearance" is critical if investigators are to be able to do their jobs.

"The credibility of the department's investigative organizations and disciplinary system depends on that independence, yet the perception exists among knowledgeable parties that external influences have negatively affected some SID investigations," the report said.