MOSCOW — The Russian intelligence officers indicted on Friday by the United States special counsel, Robert S. Mueller III, served in a branch of the Russian military formerly known as the G.R.U., which has been linked in recent years to a number of increasingly bold, even reckless operations abroad.

The organization is Russia’s largest military intelligence agency and is one of several groups authorized to spy for the Russian government, alongside successor agencies to the K.G.B.

Though the G.R.U. has been the target of sanctions by the United States government numerous times, including in connection with hacking in the 2016 presidential election, the indictments filed by Mr. Mueller’s office are the first criminal charges leveled against Russian government officials for election meddling.

A previous indictment the financier and employees of a nominally private internet troll farm based in St. Petersburg.