I use invisible IFRAME tag with HTTPS protocol for
remote scripting like

<span id="SPANjsrs1" style="display:none">
<iframe name="jsrs1"></iframe></span>
<script>
container=window.frames['jsrs1'];
...

During page load containing this tag causes every time annoying prompt in IE

This page contains both secure and unsecure items. ...

How to remove this prompt ?
I cannot instruct all web users to change their browser settings.

Adding a src="dummy.htm" attribute to iframe tag helps but this
causes extra access to web server.

How to do this without having extra server access ?