yes, in safari browser, when you will try to change the src property, nothing will happened, but to overcome the issue, you need to generate the whole iframe in code and then assign that iframe to some div, this will resolve the issue
here is the sample code
<div id="containFrame" runat="server">
public void GenerateFrame(string urlsrc)
string frame="<iframe id='ifrm' style='width: 956px; height: 500px'";
frame += " src='"+urlsrc+"' ></iframe>";
containFrame.innerHtml = frame;
i wrote this code directly on post, so if there is some mistake, then let me know again.