Dunno if its true or not, but according to this report, the marines were hit by mortars and were actually doing some fighting it seems:

http://af.reuters.com/article/libyaNews/idAFL5E8KCMYB20120912?pageNumber=1&virtualBrandChannel=0

May have to retract my former statement.

Marines and Libyan military were both protecting our ambassadors.  But these weren't protestors, these were a focused, out for blood murder crew armed with RPG-7's and feinted security to get the embassy staff in position to snipe them with high explosives.  This was their sick 9/11/01 "celebration," and the Libyan units who lost their friends are already hunting for the banned organization that made the attack.  It's going to be like killing a cop - the Libyans are going to want blood for their friends, which is why publically, we're only sending eye-in-the-sky drones.