FBI agents searched the Watergate apartment of Robert McFarlane for evidence of his alleged connection with Sudan, CNN reported Thursday.
Sudan is under strict U.S. sanctions and a trade embargo for its support of terrorism and violations of human rights.
A two-year investigation into McFarlane resulted in the discovery of email messages to the former Reagan adviser from someone in the Sudanese intelligence service, CNN reported.
"I believe these emails are evidence that McFarlane was entering into an agreement with the government of Sudan to lobby the U.S. government officials on behalf of Sudan and to provide it with advice during negotiations with the United States," FBI agent Grayden Ridd said in a court document.
Ridd said the documents further indicated McFarlane's Sudanese contact wanted to structure a deal so it appeared as though McFarlane was representing U.S. ally Qatar.
McFarlane's lawyer, Barry Levine, said McFarlane is cooperating with the investigation, though maintains his innocence. No charges have been filed against him.