Senate Select Committee on Intelligence Chairman Richard Burr, R-N.C., said allegations that employees of Hillary Clinton's State Department engaged in quid pro quo are "serious."

"We continue to debate this matter solely because Secretary Clinton and her team deliberately chose to set up a personal server on which to conduct official, and often classified, government business," Burr said in a statement Monday. "The allegations of a potential quid pro quo are serious. It is our understanding that these conversations are being reviewed further, as they should be."

Newly released documents from the FBI's investigation of Clinton's email server suggest State's undersecretary for management Patrick Kennedy reportedly " pressured" the FBI to alter classified markings on an email labeled "secret." A witness told the FBI that he "believes State has an agenda which involves minimizing the classified nature of the Clinton emails."

"Classified information was transmitted, as other government agencies have confirmed," Burr said. "State Department knew it, Patrick Kennedy knew it and yet they continue to fight it."

State Department spokesman Mark Toner said Monday, "Any real assertion that this was somehow a tit-for-tat quid pro quo exchange in that manner frankly is insulting." He also questioned the accuracy of the interviews conducted by the FBI.