"Those who stayed in Syria have been eliminated. Only sleeper cells remain there," an informed Russian source told Interfax, an independent major news agency in Russia.
Chief of Russia's GRU military intelligence agency Igor Korobov died on Wednesday after "a serious and long illness.
Pentagon has been slow to protect major weapon systems from cyber attacks and routinely found critical vulnerabilities that hackers could potentially exploit.
Jeremy Hunt accused Russian military intelligence of conducting a campaign of "indiscriminate and reckless" online attacks targeting political institutions.
Two men accused by London of poisoning former Moscow spy Sergei Skripal denied being involved with the murder attempt in a bizarre Russian media interview.
Washington it would impose fresh sanctions on Russia by the end of August after it determined that Moscow had used a nerve agent against a former Russian agent.
Twelve Russian intelligence officers have been charged with hacking Hillary Clinton's 2016 presidential campaign and the Democratic Party.
Russian military intelligence officers were indicted by a US grand jury -- just three days before President Donald Trump's meeting with Russia's Vladimir Putin.