How to delete chat history in battlelog chat ?

I can't find anywhere on the net - how in the hell can I delete the chat history in Battlelog ? I have some old chat content that I don't want to see every time I open the chat with my friend. I can't find a way to delete the chat history. I even tried to unfriend him and befriend him again, and that old portion of chat messages is always there. Please make it dissapear, or at least put some option to do so myself. Is it related with the cache clearing from the browser itself ? I have some browser history I don't want to delete, but if it takes that to do so, I will. I just don't want to try just to find out that it was in vein. Thanx in advance for your help.