The armed drone that was shot down by a U.S. Air Force F-15 in southern Syria Thursday was almost certainly from Iran, but you won't hear anyone say that at the Pentagon.

"I don't think we're ready to call it that, but at the very least its evidence of Iran's influence there," was as close as Navy Capt. Jeff Davis, a Pentagon spokesman, would get.

But the U.S. military has provided enough clues that anyone with a rudimentary knowledge of the region's armament can figure out whose drone it was. First, officials described it as a knock-off of a U.S. Predator, America's first generation of armed drones.

"It was the same size as our MQ-1 Predator. It was kind of like that," said Col. Ryan Dillon, a U.S. military spokesman in Baghdad right after the attack.

The drone dropped what turned out to be a "dud munition," but still had other armaments when it was shot down.

At the Pentagon, Davis noted that the unmanned warplane was operating in support of Iranian-backed militia on the ground, who have been challenging a U.S.-declared de-confliction zone surrounding a training base near the Syria-Iraq border.

"We do know that Iran, obviously in its support for the regime, provides them with equipment, provides them with assistance and support with funding," Davis said.

A U.S. military official gave the Washington Examiner another clue, confirming the drone came from a "country in the region," not Russia.

A country in the region plus a drone that looks like a U.S. Predator add up to Iran's Shahed-129, a Predator-lookalike, which is the only armed drone in Tehran's arsenal and far too sophisticated to be operated by the Islamic State, or some militia group.

"There are not a lot of players on the battlefield that operate this kind [of drone]," Davis said. "This is not a quadcopter. This is a significant high-end fighting system, and there's not a lot of players who operate it."

So if Iran is the only likely suspect, and if the drone attack posed a real threat to coalition and U.S.-backed partner forces, why not call Tehran out?

"We're not looking to start a fight with anybody else, other than ISIS," Davis said. "But we acted in self-defense, and if it happens again, we'll act again."