How to block outgoing calls to a specific country on Asterisk?

[Leo]

Hi, I have a simple Asterisk server running, and I'd like to block
calls, in all the VoIP providers I have in my Asterisk, to a specific
country. My current dial plan for outgoing calls is this:

exten => _2X.,1,Dial(SIP/${EXTEN:1}@callcentric-out)
exten => _2X.,2,HangUp

exten => _4X.,1,Dial(SIP/${EXTEN:1}@sipgate-out)
exten => _4X.,n,HangUp

exten => _5X.,1,Dial(SIP/${EXTEN:1}@voipdiscount-out)
exten => _5X.,n,HungUp

It's relatively hard to find "easy" information on Asterisk, not many
example configs around there, and I'm try to do a very simple setup to
use VoIP in my house, but this has been giving me a headache (not so
much, hehehe), and I appreciate any help I could get...

Thank you,

Leonel Viotti