<IfModule mod_rewrite.c>
    RewriteEngine On

    RewriteCond %{REQUEST_METHOD} POST
    RewriteCond %{REQUEST_URI} ^(.*)wp-comments-post\.php*
    RewriteCond %{HTTP_REFERER} !^(.*)in.rs.*
    RewriteCond %{HTTP_REFERER} !^http://jetpack\.wordpress\.com/jetpack-comment/ [OR]
    RewriteCond %{HTTP_USER_AGENT} ^$
    RewriteRule ^(.*)$ - [F]
</IfModule>