Western intelligence officials say the unit, which has operated for more than a decade, has been charged by the Kremlin with carrying out a campaign to destabilize the West through subversion, sabotage and assassination. In addition to the 2018 poisoning, the unit was behind an attempted coup in Montenegro in 2016 and the poisoning of an arms manufacturer in Bulgaria a year earlier.
American intelligence officials say the G.R.U. was at the center of Moscow’s covert efforts to interfere in the 2016 presidential election. In the months before that election, American officials say, two G.R.U. cyberunits, known as 26165 and 74455, hacked into Democratic Party servers and then used WikiLeaks to publish embarrassing internal communications.
In part because those efforts were aimed at helping tilt the election in Mr. Trump’s favor, his handling of issues related to Russia and Mr. Putin has come under particular scrutiny. The special counsel investigation found that the Trump campaign welcomed Russia’s intervention and expected to benefit from it, but found insufficient evidence to establish that his associates had engaged in any criminal conspiracy with Moscow.
Operations involving Unit 29155 tend to be much more violent than those involving the cyberunits. Its officers are often decorated military veterans with years of service, in some cases dating to the Soviet Union’s failed war in Afghanistan in the 1980s. Never before has the unit been accused of orchestrating attacks on Western soldiers, but officials briefed on its operations say it has been active in Afghanistan for many years.
Though Russia declared the Taliban a terrorist organization in 2003, relations between them have been warming in recent years. Taliban officials have traveled to Moscow for peace talks with other prominent Afghans, including the former president, Hamid Karzai. The talks have excluded representatives from the current Afghan government as well as anyone from the United States, and at times they have seemed to work at crosscurrents with American efforts to bring an end to the conflict.
The disclosure comes at a time when Mr. Trump has said he would invite Mr. Putin to an expanded meeting of the Group of 7 nations, but tensions between American and Russian militaries are running high.
In several recent episodes, in international territory and airspace from off the coast of Alaska to the Black and Mediterranean Seas, combat planes from each country have scrambled to intercept military aircraft from the other.
Mujib Mashal contributed reporting from Kabul, Afghanistan.