---------------------------
Add this to .htaccess file
---------------------------

<Files wp-login.php>
  order deny,allow
  deny from all
  allow from xxx.xx.xx.xx
</Files>


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To allow multiple IPs use the following:
----------------------------------------

<Files wp-login.php>
order deny,allow
deny from all
allow from xxx.xx.xx.xx
allow from xxx.xx.xx.xx
</Files>