It seems to be saying that they want to see some action, but that they do not want to see a military strike, as that would be going overboard and doing more harm than good.
I think that saying "but it's not necessarily a military strike, mind you" sort of misses the mark a little bit, and conveys the idea that the operation they have in mind is even more threatening than an ordinary military strike, like a nuclear missile or something.
As a replacement for "just", I think "mind you," and "but" both provide good approximations, but I don't think that "mind you" without a comma is any good, as in @dcaswell's answer
I also do not agree at ALL that the original version sounds awkward, speaking as a native Australian speaker.
"Without concession by" does not mean "according to".
The most likely interpretation (as pointed out by FumbleFingers in comments) of the (ridiculously long and complex) sentence is that:
Exploitation (...) should be penalized-without-concession by the national legislation.
Here we see that "without concession by" is not actually a phrase. "By" is a preposition connecting the verb-phrase "penalized-without-concession" to it's subject, the "national legislation" (an awful noun meaning in this context the body that enacts penalisation, rather than the written laws that "legislation" would normally mean).
And the phrase "without concession" means "without reducing the penalisation for any reason - without conceeding that there might be a reason to reduce it"
Another different interpretation of the sentence (my initial interpretation) is that the sentence was trying to sat that the "State concerned" should prosecute and penalize exploitation even if the national legislation in the visited country allows exploitation, and hence would allow concession. The States concerned should not "make concessions to" the national legislation, nor allow concessions by the national legislature, they should stick to their own position and prosecute to the full force being proposed. In this interpretation, the State is doing the penalisation, and the direction of the statement is that the State should not allow concession by the national legislation.
Both interpretations are similar in that the phrase "without concession" is telling us that no matter who is doing the penalization, it should be to the full extent possible.
Best Answer
In the first part of the sentence, the author is merely stating how France and other countries think that the proposals are infringements on national sovereignty. In the second part of the sentence, the author is proclaiming full agreement with that position.
It would be similar to if I said:
The second part of that sentence shows that I agree: it's indeed a good question. Were that not my belief, though, I might write instead: