WASHINGTON — A Pentagon counterterrorism analyst shared classified information with two journalists for more than a year, one of whom he was dating, according to an indictment unsealed on Wednesday.

The analyst, Henry Kyle Frese, 30, was arrested on Wednesday at his office at the Defense Intelligence Agency, where he has worked since January 2017, first as a contractor and then as an employee, prosecutors said.

His arrest was the latest in the Justice Department’s aggressive efforts to crack down on illegal leaks of classified information. Six people have been charged with unlawfully sharing government information since Jeff Sessions, then the attorney general, vowed in August 2017 to ramp up the fight on leaks, said John Demers, the head of the department’s National Security Division.

Until 2017, no one had been charged in leak cases since 2013. Law enforcement officials under President Barack Obama prosecuted more leak cases than all previous administrations combined.