Really hope this doesn't mean a ground invasion in the near future.
If you're announcing that you'll kill surrendering Iranians, it seems to follow that you intend to kill lots of Iranians and are not particularly concerned with the ethical implications.
Aren't we already?
The current administration has torched relationships with essentially every allied country except Israel. From Toronto to Taipei, and across NATO and BRICS, people see the US as a chaotic bully to be dealt with, not a friend or role model.
I don't think that "other countries won't like it" carries any significance at all to the people in power.