Take a look into using something like mod_geoip if your using Apache.
Yes - this (^)
If Apache is compiled with mod_geoip, then the country code of the visitor (as determined by the data file that your host has supplied) is visible through Apache.
You can then put this in your .htaccess
SetEnvIf GEOIP_COUNTRY_CODE CN BlockCountry
SetEnvIf GEOIP_COUNTRY_CODE RU BlockCountry
Deny from env=BlockCountry
That would block all visitors from China and Russia - purely as an example.
That line wouldn't break anything if the server doesn't have mod_geoip, because the IfModule section only applies the code if the relevant module is loaded. But you may want to ask your host if this is something they've got set up on the server.