Permissibility to kill all adult males

Is it permissible to kill all men from the kuffar when a city or a land have been conquered by muslims, there will be men who actually fought against the muslims and there will be some men who never participated in the fight but rather they were just civilians or non combatants who did not resist the muslims advancement into a said city or land, so are these type of men permissible to be killed while advancing or after being captured? I am not talking about old,sick or other types of men mentioned in hadith but men who are capable of fighting and are sane but did not actively participate in war