Federation and Klingon War Crimes
The Klingons are attacking Corvan II, which is apparently where much of the Federation's dilithium comes from. They are certainly within the laws of war to attack a strategic supply of a needed item of their enemy, but there are civilians on Corvan II and Klingon tactics are illegal! The Klingon bombardment is clearly violating interstellar legal norms because they are not targeting specific points. Generally, for attacks from space to ground, the operations must comply with the galaxy-wide recognized principles of military necessity, distinction, and proportionality.1
The military necessity of attacking the dilithium processing facilities seems obvious. However, the Klingons are bombing the entire area, and are not discriminating between civilian and military personnel, nor is their act proportional to a previous Federation attack, or to the facility specifically.
Interestingly, it is also generally acknowledged that even though the attacking forces must take precautions to protect the lives of civilians, the defending forces must also avoid locating military objectives near or in densely populated areas, and must try to remove civilians from near military objectives. Most civilizations have codified rules against this as we do, but there are many historical examples of this sort of activity being frowned upon. It wasn't that long ago that the Vulcans used the monastery on P'Jem to hide a surveillance station.2 And the Andorians terraformed an D-class planetoid and filled it with "colonists" in order to lay claim to a region of space and be a thorn in the side of the Vulcans.3 Both actions were seen to violate interstellar norms.
So, it is against the rules for the Klingons to bomb the dilithium sources as long as there are civilians there. But it is also against the rules for the Federation to have civilians at a legitimate military target. I guess there really are "bad actors on both sides."
1 See Gomez, Javier Guisandez, "The Law of Planetary Bombardment,"Interstellar Review of the Red Cross (June 20, 2198).↩
2 See Logs of Captain Archer, NX-01 Enterprise "The Andorian Incident" (June 19, 2151).↩
3 See Logs of Captain Archer, NX-01 Enterprise "Cease Fire" (2152).↩