Definition: In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].
Input: (CNN) -- The U.S. military said it is investigating claims from Syria that U.S. helicopters based in Iraq killed eight people and wounded another Sunday in an attack inside Syria's territory Sunday. A U.S. army Apache helicopter flies over southern Baghdad, Iraq. Syria's state news agency SANA said four U.S. helicopters crossed the border and struck a farm about 8 kilometers (5 miles) inside Syria before returning to Iraqi airspace. The raid occurred about 4:45 p.m. (1345 GMT). The helicopters hit a civilian building under construction on the farm, killing a father and his four sons, a married couple and another man, SANA said.State news agency says 3 men, 1 woman, 4 children killed near Iraq-Syria borderSANA says 4 helicopters from Iraq crossed border about 5 miles into Syria, hit farmSyrian government summons U.S., Iraqi diplomats to Foreign Ministry in DamascusU.S. Military says it is investigating claims, cannot confirm anything right now 
 Question:Syria demanded _'s government "immediately investigate this serious violation" and bar U.S. forces from striking Syria from its territory.

Iraq