WASHINGTON (Reuters) -The United States and Britain on Monday imposed sanctions on a network of people who targeted Iranian dissidents and opposition activists for assassination at Iran's direction, the U.S. Treasury Department said on Monday. The U.S. Treasury in a statement accused the network of being directed by Iran's Ministry of Intelligence and Security and put sanctions on 11 people connected to it, including Iranian narcotics trafficker Naji Ibrahim Sharifi-Zindashti, who it said is the leader. The Treasury said Zindashti’s network had carried out assassinations and kidnappings across a number of jurisdictions, aiming to silence Tehran's perceived critics.