[Illuminated One]

I'd say it's a grey area, like many things concerning NAPs.
A NAP is nothing more than an oral (laugh at me if that's a wrong translation) contract with noone to enforce it in game and can be interpreted however you like - just like real life contract between nations. So your country was hit by Missiles manufactured by your long-term ally?
=> It's up to you wether to cancel all agreements, seek a diplomatic sollution, or just focus on killing the guy who can pay for the missiles.

If there are specific game rules you can ask the admin to enforce it, because of this it is good to ask about game NAP rules before you enter one.