WASHINGTON—A Russian spy device paid out members of Afghanistan’s Taliban movement to conduct lethal assaults on U.S. troops in that place, according to a classified American intelligence assessment, people today common with the report explained.

The assessment of the part performed by Russia’s armed service intelligence company, the GRU, in fostering assaults on American troopers, will come as President Trump is pushing the Pentagon to withdraw a important portion of U.S. forces from Afghanistan and as U.S. diplomats consider to forge a peace accord involving…