what's the meaning of "friend and foe'?

what's the meaning of "friend and foe'?
Potter bent down and trained his Leica field glasses through the thick windows.He studied the slaughterhouse.A skull [头盖骨] of a building.Stark against the sun-bleached grass,like dried blood on yellow bone.That was the assessment of Arthur Potter English lit [literature] major.Then,in an instant,he was Arthur Potter the Federal Bureau of Investigation’s senior hostage negotiator and assistant director of the Bureau’s Special Operations and Research Unit,whose quick eyes noted relevant details:thick brick wall,small windows,the location of the power lines,the absence of telephone lines,the cleared land around the building,and stands of trees,clusters of grass,and hills that might provide cover for snipers—both friend and foe.
Question:
At the end of the paragraph,the author wrote “both friend and foe”.This phrase is to describe what Arthur Potter has observed.Explained in your own words,what does he mean by friend and foe.The explanation should not exceed three sentences.