Authorities in Yemen have seized a boat in their territorial waters filled with a large quantity of explosives, weapons and money. The officials said there were indications that Iran was smuggling the military contraband to insurgents inside Yemen. 

The captured weapons included surface-to-air missiles used to shoot down civilian and military aircraft, C4 military-grade explosives, 122-millimeter shells, rocket-propelled grenades and bomb-making equipment, including electronic circuits, remote triggers and other hand-held explosives. 

With the United States and Saudi Arabia providing both public and secret security assistance there, and with Iran also said to be arming militant forces, Yemen has become the battlefield for a major proxy war by outside powers. 

American officials said the weapons on board were made in Iran, and that the pattern of the shipment matched past instances of suspected Iranian smuggling into Yemen. Officials described the smuggling as part of a plan by Iran to increase its political outreach to rebels and other political figures in Yemen. 

This interdiction comes at an extremely delicate time in Yemen, with the government largely paralyzed, sectarian tensions rising and accusations of Iranian interference — which have long been used as a propaganda tool here — on the increase.