WASHINGTON — The authorities in Yemen have seized a boat in their territorial waters filled with a large quantity of explosives, weapons and money, according to American officials briefed on the interdiction. The officials said Monday that there were indications that Iran was smuggling the military contraband to insurgents inside Yemen, although they declined to provide details.

Yemeni security forces halted and searched the sailboat, a 130-foot dhow, last Tuesday and found the weapons in three large cargo rooms in the hold, according to reports on the mission reaching Washington. There was American support for the interdiction, officials said.

The government of Yemen confirmed the seizure Monday in an official statement. 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, the statement said.

If the weapons turn out to include the Iranian-made Misagh-2 surface-to-air missile, as cited in the reports from Yemen, it would reflect a significant increase in lethality for the insurgents. Yemen is already awash with small arms and explosives acquired over years of war and insurgency, much of it brought in from a number of foreign sources through its poorly controlled ports. There has been little effort to regulate the supply — one governor of a northern province is also a major arms dealer — and insurgents have often raided the stores of Yemen’s corrupt and divided military. Many of Yemen’s unruly tribes command powerful arsenals.