NEW DELHI, Feb. 17 -- India has seized three US-sanctioned tanker ships linked to Iran this month and stepped up surveillance in its maritime zone to curb illicit trade, a source with direct knowledge of the matter said on Monday. India aims to prevent its waters from being used for ship-to-ship transfers that obscure the origin of oil cargoes, the source added. The seizures and heightened surveillance follow an improvement in U.S.-India relations. htc...