According to the US Navy, it has confiscated a million rounds of ammunition as well as rocket detonators and fuel that were supposed to be smuggled from Iran to the war-torn Yemen on a fishing boat.
The cargo was discovered during an inspection on Thursday, the US Navy's fifth fleet, based in Bahrain, said on Saturday.
It is the second "major confiscation of illegal weapons within a month" on this sea route.
The incident shows "clearly" that Iran continues to "illegally" supply arms to Yemen, thereby destabilizing the region, Vice Admiral Brad Cooper said.
The US Navy will therefore continue to focus on "preventing and suppressing dangerous and irresponsible maritime activities in the region".
In Yemen, war is raging between government forces backed by Arab states and Houthi rebels, backed by Iran.
A ceasefire negotiated by the UN reduced the fighting.
However, it expired in October.
"The direct or indirect supply, purchase or transfer of arms to the Houthis of Yemen violates UN Security Council Resolution 2216 and international law," the US Navy said.