Eliot Engel, chairman of the House Foreign Affairs Committee, wrote a letter Wednesday to the State Department seeking records related to Hyde, Parnas and Yovanovitch. Engel wrote that he was especially alarmed by messages in which Hyde suggested he had “a person inside” who could offer information on the ambassador; Engel questioned whether that person could be based at the U.S. Embassy in Kyiv.

“This unprecedented threat to our diplomats must be thoroughly investigated and, if warranted, prosecuted to the fullest extent of the law,” the New York Democrat said in a statement earlier in the day.

Engel also said his staff had contacted the State Department division that handles diplomatic security to “seek assurances that proper steps have been taken to ensure the security of Embassy Kyiv and that of Ambassador Yovanovitch.” Without offering details, Engel said he’s “confident this matter is getting the attention it merits.”