Make twitter widget links act external


I am using the twitter widget in my site, but I need to be able to put a class on each tweet so that I can mark these as external links (put an icon on them and give a message when they are clicked.

How can I add a class to each tweet? this is my code:

<a class="twitter-timeline ext"  data-chrome="nofooter noscrollbar noborders nofooter transparent"    href=""  data-widget-id="[widget-id]" target="_blank">Tweets by @FAFSA</a>
    <script>!function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0],p=/^http:/.test(d.location)?'http':'https';if(!d.getElementById(id)){js=d.createElement(s);;js.src=p+"://";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs");</script>