[ikeboy]

There would be no legal basis for such a prohibition, as there's no plausible national security endangerment were the request to be revealed.

[DKnoll]

Haven't you seen Men in Black?

[nickpsecurity]

Well, less ignore mass panic and such. It's always been US government policy not to talk about these things. Canadian and UK, too, apparently. So, it being classified mighg make it a no go.

However, I found this Quora answer to give pretty good justification on national security grounds for military scenarios:

https://www.quora.com/Why-is-the-government-afraid-of-reveal...