2007 film by Jaume Balagueró and Paco Plaza

Captain Martin Stone is leading a finely-trained, elite platoon of Allied soldiers as they attack an enemy bunker. Underestimating their enemy's strength, they are quickly beaten back into the forest. As they try to regroup, they are suddenly attacked by the same soldiers they had just killed a few minutes earlier. Forced to flee deeper into Russian territory, they discover one of war's most terrifying secrets and realize they have woken up a far more deadlier enemy.

U.S. federal agent Leon S. Kennedy sneaks into the "East Slavic Republic" to verify rumors that Bio-Organic Weapons (BOWs) are being used in the country's civil war, which the U.S. and Russia are making preparations to jointly intervene in. Right after his infiltration, the U.S. government orders him to leave immediately. Determined to uncover the truth, Leon ignores the order and enters the battlefield to end the chain of tragedies caused by the BOWs.