I don't believe we "promised" anything of the sort, but even if we did, there is no reason to "apologize." The Japanese have not taken any casualties. What exactly are we to apologize for? Japanese troops and civilians being unable to visit Iraq with the same sense of safety as if they visited London or Paris? I think the Japanese involved will be quite happy to stay home rather than go to that pesthole, personally.
It's one thing to be diplomatic, another to be realistic. There's nothing to apologize for, if the Japanese don't want to go, that's their affair and they can stay home. They have not been harmed.
Fair enough. I don't begrudge them their freely made decision.