Outside law enforcement experts are looking into how the State Department investigates allegations of sexual crimes and other serious misconduct by diplomats, amid charges that senior officials have improperly halted such probes.

The department said Tuesday that its internal watchdog, the Office of the Inspector General, had contracted with former law enforcement agents to review the process and determine whether investigators in the Bureau of Diplomatic Security have the independence necessary to do their jobs effectively. Officials said the review was expected to be complete later this summer.

The review was ordered after at least one investigator complained 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.

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

“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 memo contained “unsubstantiated accusations” about both improper behavior by diplomats and interference into investigations and was “written without the benefit of reviewing any case files,” Psaki said. She added that by the time the memo was written in October 2012, investigators “had already started looking into or completed the process of looking into these individual incidents.”

“All of these cases have been or will be brought to their logical conclusions,” she said.

The New York Post on Tuesday reported more details of the allegations in the memo, 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 of the specific cases mentioned in the memo, citing privacy considerations involving personnel records.

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