Dutch and German intelligence agencies have gathered evidence of widespread Russian use of banned chemical weapons in Ukraine, including dropping a choking agent from drones to drive soldiers out of trenches so they can be shot, they said on Friday. Dutch Defence Minister Ruben Brekelmans called for tougher sanctions against Moscow. The United States first accused Russia of using chloropicrin, a chemical compound more toxic than riot control agents and first used by Germany during World War One, in May last year. Ukraine alleges thousands of instances of Russian chemical weapons use.