WASHINGTON — Iran has developed a new type of antiaircraft missile and shipped it to Houthi rebels in Yemen, Pentagon officials announced Wednesday. The weapons were seized by United States Navy warships in two separate shipments in the Arabian Sea.

In a news briefing, Capt. Bill Urban, a spokesman for Central Command, declined to comment on how the missiles worked. But a military official familiar with the weapons, referred to as 358 missiles, described them as cruise missiles that are designed to avoid United States defensive measures and that can down American military helicopters, as well as the tilt-rotor MV-22 Osprey.

The missiles consist of three parts: two motors and an explosive warhead. The weapon can be assembled after shipment and fired from a crude launcher on the ground. Once the missile is fired and traveling fast enough, a solid-fuel boost motor falls away and a cruise motor takes over; at that point, the weapon flies in a figure-eight pattern and looks for targets.