They’re never going to admit that the drones are US military assets. Admission would be detrimental to the operational security, and would likely be an admission of their purpose.
So far, we’ve had multiple theories. However, deduction and reasoning have granted us the opportunity to make an assessment. The drones are located either over VIP locations, critical infrastructure, or ports-of-entry. This would never be tolerated, so that is our answer as to whose they are—US.
Their purpose is akin to their locations. They are searching for something in a defensive posture. As such, they give away their purpose.
The moment Assad left Syria, these drone sightings multiplied quickly. Iran, having a major political issue, and also a cultural hatred as well, tried to kill Assad by taking his plane down. Israel is also a possible suspect. Russian assets ensured the Assad family escaped via covert means.
The drones are looking for nuclear material. The problem is that they aren’t looking in one spot as if they know exactly where one or more are. This means, logically speaking, there must be multiple WMDs on US soil.
Iran may be the culprit. However, the Samson Option is still at play. Israel may be so close to losing their grip on the US that they, or Iran, may be planning another massive 9/11-like atrocity.