Declaring that no quarter will be given unequivocally violates international humanitarian law. Indeed, ordering that no quarter will be given, threatening an adversary therewith or conducting hostilities on this basis is prohibited and constitutes a war crime.
Oona Hathaway
Hegseth: "We will keep pushing, keep advancing. No quarter, no mercy for our enemies."
No quarter is the refusal to take prisoners and instead just execute everyone. It's been considered a war crime for over a century.