So, here goes : the call sign is useless but the craft apparently took off from Malta and it's mode-s address is ae5413 making it an American aircraft.

One site associates the mode-s address with call sign/flight-number UAVGH000 and that is a big clue indeed ! That's a call sign/flight-number used for NATO RQ-4D Global Hawks. So that would identify the type of craft !

Another site appears to confirm there are indeed RQ-4Ds flying from Malta listing a number of sorties both in this and last month. It identifies the RQ-4D as MT-AV-SA-0016. So now we have type and registration.

But ! Malta is close enough to Sicily and Sigonella specifically where we know for a fact RQ-4Ds are stationed. The trackers could have mistaken Sigonella for Malta, they often mistake Sigonella for Catania as they appear to pick the first known airport nearest to the coordinates of the first ADB-S message. On top of that there is an RQ-4A stationed at Sigonella with serial-number/registration MM-AV-SA-0016 as opposed to MT-AV-SA-0016, and it has flown a couple of times now with call sign/flight-number UAVGH000.

Nevertheless I think the circumstantial evidence as well as the political climat involving the Trump administration's relation with NATO and Malta's relation with NATO is strong enough to say : yes, the US is conducting at least test flights with the NATO variant of the RQ-4 from Malta. The other US military and government flights then become part of the effort, personnel etc required to set up this operation.