Debris gathered from the drones and missiles used to attack an oil field and refinery in eastern Saudi Arabia increasingly lends credence to US and Saudi accusations that Iran was in some way behind the attacks. Other evidence presented thus far also suggests that the attacks may have been launched from Iran rather than Yemen, as the leadership of the Houthi militia fighting Saudi Arabia there has claimed.
A total of 25 drones and missiles were used in the attack. The missiles appear to have been identical to the Quds-1 cruise missile revealed by Ansar Allah (the Houthi militia) in a weapons display on July 7. The drones were delta-winged, propeller-driven unmanned aircrafts with stabilizer fins at the tips of each wing.
Quds it be?
The Quds-1 is a smaller missile than the Soumar—Iran's clone of a Soviet-era cruise missile obtained from Ukraine in 2001—and its latest iteration, the Hoveyzeh. The Quds-1 uses what appears to be a Czech-built turbojet engine, the PBS Aerospace TJ100 (which PBS advertises as "especially suitable for unmanned aerial vehicles") stuck onto its upper fuselage for propulsion.
Based on analysis of photographs and other evidence, Fabian Hinz of the James Martin Center for Nonproliferation Studies and others have posited that the Quds-1 was used in the September 14 attacks. A TJ100 engine was found in the wreckage, and the missile had a smaller diameter than the Soumar, with rounded control fins identical to those in photos of the Quds.
This doesn't get Iran off the hook for the attack. Drones displayed by Iran have had TJ100 turbojets (or engines that are nearly identical knockoffs). And the Houthi Ansar Allah, while having some technical capabilities, would be hard-pressed to produce turbojet engines—let alone an entire cruise missile with terrain following systems and satellite navigation.
There's a possibility of an even more direct Iranian connection: while the Soumar would have plenty of range to be launched from Yemen and strike northeastern Saudi Arabia, the TJ100 has significantly less thrust and is less fuel efficient than the engine used in the bigger missile. In order to reach its target, it would more likely have had to been launched from southwestern Iran. While Iran has not publicly displayed the Quds-1 under any name, it is likely that it is a simplified weapon built specifically for Iran's proxies, just as Iran has done with some drone weapons.