Standard ROE in Afghanistan and Iraq requires you to PID (Positive Identification) all targets before you open fire. PID means that not only must you be under fire, you can only return fire if you can see the individual(s) firing on you. If they're behind a bush, or in a dark room in a building you cannot return fire.
I'd like the military manuals but reddit gets butthurt when you try to link PDFs. But if you search "PID Afghanistan" you should get a plethora of links. Here are the 5 requirements:
Understand the Relationship of Self-Defense and Tactical-Level Fires to Rules of Engagement and Fire Support Control Measures.
Under the OEF and OIF ROE, certain categories of targets could not be engaged without the approval of certain high levels of command. The categories and approval levels are classified. The CENTCOM CDEM, both the OEF and OIF versions, set forth a targeting methodology that, in its simplest form, distilled targeting decisions into five unclassified, sequential questions, the fifth of which represents the issue at hand.
Can I positively identify the object or person I want to attack as a legitimate military target authorized for attack by the current rules of engagement?
Is there a protected facility (i.e. No Strike), civilian object or people, or significant environmental concern within the effects range of the weapon I would like to use to attack the target?
Can I avoid damage to that concern by attacking the target with a different weapon or with a different method of approach?
If not, how many people do I think will be injured/killed by my attack?
Do I need to call my higher commander for permission to attack this target?