Secretary of State Rex Tillerson's team on Thursday rejected Russian complaints about the search of three facilities taken by the U.S. government and said the U.S. invited Russian officials to observe the process.

"Russian officials were invited to come along with us as we toured those facilities last weekend," State Department spokeswoman Heather Nauert told reporters Thursday. "They chose not to accompany us on the New York walkthrough, for whatever reason. I simply do not know. It is certainly in our authority to be able to look around and I'll just leave it at that."

Tillerson ordered the closure of three facilities in the United States as part of a diplomat spat that traces back to U.S. sanctions punishing the interference in the 2016 elections. Nauert rejected Foreign Ministry complaints about the process, which her counterpart dubbed "an illegal invasion" of sovereign Russian territory, and said State Department officials conducted less-aggressive "searches" or "inspections."

But she also offered a mild rebuke of American reporters who focused on the process. "I don't know if you all are working for RT today or what," Nauert said with a laugh. "I don't know the normal process for going through those facilities, but I will look into it."

That comment was a reference to a Russian state-run media outlet that U.S. intelligence officials have identified as an organ for propaganda pertaining to the 2016 cyberattacks against the Democratic party.

Nauert emphasized that the FBI was not involved in the searches, despite Russian claims. She also declined to say if the searches were motivated by a concern that the buildings were used for intelligence purposes or other activities not covered by diplomatic agreements.

"I'm just not going to get into that," Nauert said. "Some of these matters, I'm not going to get into and debate with you here from the podium. When I can give you additional information, I certainly will and would be happy to."