I would argue that it is dishonorable to target the citizenry of a nation whose government is one's enemy. A couple of points are in order here:

(1) There is a vast difference between the deeply regrettable, yet unavoidable collateral damage--a term that is a bit more antiseptic than I would prefer; but I cannot think of a better substitute--that is inevitable in wartime, and the intentional targeting of civilians. The moral distinction should be so obvious as to require no elucidation.

(2) The bombing of Hiroshima and Nagasaki in 1945 is a tough case. The Japanese citizenry--including even women and children--certainly had done nothing to deserve such a horrendous fate. But the sudden use of Fat Man and Little Boy to bring the war in the Pacific to a quick halt may actually have saved more civilian lives than it cost. This is because of the likelihood of Japan's engaging in house-to-house combat for a very long time, notwithstanding the attempts of revisionist historians to claim that this would never have happened. In the end, therefore, I am highly ambivalent about this one.

I don't see anything dishonorable about either. Which are you suggesting is likely to be Iran's course of action?

No, that is not inherently unethical; especially if (a) the other country has widely advertised its intention to destroy another nation in the neighborhood, whose right to exist it refuses to recognize (presumably with the nukes that it currently has under development; and with which it would intimidate and blackmail other Western nations); and (b) it is in the process of murdering the other country's soldiers--not killing them in combat, but murdering them with roadside bombs.