The FBI on Sunday issued the strongest warning to date about possible attacks by the ISIS terrorist group against the U.S. military inside the homeland, officials told ABC News.

In a joint intelligence bulletin issued overnight by the FBI with the Department of Homeland Security, officials strongly urged those who serve in uniform to scrub their social media accounts of anything that might bring unwanted attention from "violent extremists" or would help the extremists learn individual service members' identities.

"The FBI and DHS recommend that current and former members of the military review their online social media accounts for any information that might serve to attract the attention of ISIL [ISIS] and its supporters," the federal bulletin sent to law enforcement agencies said, advising that troops "routinely exercise operational security in their interactions online."

Officials said they fear copycat attacks based on what happened in Canada last month, when two uniformed Canadian soldiers were killed in two separate incidents by young men who claimed they were ISIS followers.

"The FBI recently received reporting indicating individuals overseas are spotting and assessing like-minded individuals who are willing and capable of conducting attacks against current and former U.S.-based members of the United States military," the bulletin said.