KABUL — The U.S. military in Afghanistan has detected an increasing number of Russian-made small arms being used by Taliban fighters on an increasingly complex battlefield here.

U.S. military officials confirmed Monday that in the last 18 months, they have seen more weaponry from Russia in the hands of Taliban fighters, including machine guns and antiaircraft machine guns. U.S. officials have been complaining that the Kremlin has interfered in Afghanistan on the Taliban’s side, but the comments Monday marked the most serious U.S. charges yet.