I'd get them both to the vet for a check over, as random fighting can be a sign that one or the other is unwell and is getting defensive. I dont mean to worry you as im sure they're ok, just better to be safe not sorry.
As they are bunny "teenagers" they're probably starting to try and establish dominance over eachother. Then again it might just have been a tiff, my 2 regularly have a little nipping argument and then are best buds again afterwards. I'd advise taking them onto neutral territory to meet again and see how they get on. If they're ok and not fighting too much do a couple more sessions like that and then get them back onto their territory (water spray in hand to break up any fights!)
If they are stil being aggressive, I agree that you may have to seperate them for a few weeks and then start the bonding process as if they don't know eachother (poor you!)
Good luck and let us know how it goes