Factual error: In the scene where MGySgt Beckett and his female Balkan contact are in the basement weapons storage area, he is searching for a sniper-capable weapon to use to rescue Sgt Cole his captors. He holds up an old rifle and refers to it as a "Mauser, 7.92mm, best rifle the Germans made". He is, in fact, holding a Soviet era Mosin-Nagant M1891 rifle, probably chambered in 7.62x54mm.
Revealing mistake: The signs on the front of the street cars naming the route show a place in Budapest, which is kind of a long way from the Balkans where the movie is taking place.
Revealing mistake: The police cars have Balkan names (policia) but the police officers speak Hungarian.
Continuity mistake: When Petra and the black man (Beckett's partner) are in the firefight with the sniper behind the wall in the deserted city, Beckett and his partner are using over the ear receivers/transmitters. The black man first has the earpiece in, then it's not there, then it's there again.