Anoter US war in Yemen?

what is happening in yemen? i know that since the uprisings and protests in the arab world, yemen was apart of all these and i know the the people are now standing up and fighting an oppressive rule of their gov. there, but i also know that the Yemen gov is an ally of the US and is in some way helping fight "terrorism" in yemen...so my question is...who is killing who? the yemen president is killing the protestors, and the protestors are killing the gov millitants...who is the US bombing? the protestors? or just those who they deem "terrorsts"? or what?