BEIRUT, Lebanon — It may not be politically popular to raise concerns about the human rights of Islamic State fighters and their families. But the International Committee of the Red Cross, which has monitored the treatment of the wounded, prisoners and civilians in wartime for a century and a half, sought to do just that in a strongly worded statement on Thursday.

The organization is concerned about rhetoric that “dehumanizes” and “demonizes” the enemy or suggests that a particular adversary is “outside the bounds of humanity” and can be treated “as if humanitarian law doesn’t apply,” the group’s deputy director for the Middle East, Patrick Hamilton, told reporters via a telephone conference call.

Language that could appear to justify or encourage war crimes and illegal treatment of detainees has become more common on all sides of the sprawling conflicts in Syria and Iraq, Mr. Hamilton said, to the point that the Red Cross felt it necessary to remind all combatants that international law requires due process and humane treatment of detainees “with no exceptions.”

His comments come as the Islamic State, also known as ISIS, ISIL and Daesh, is surrendering more territory to an array of government and militia forces. Several Western officials have said that it would be best if their citizens who have fought with the Islamic State died in combat.