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) Forces aligned with Syrian President Bashar al-Assad made an incursion Wednesday into the 55km "de-confliction zone" surrounding the US base located at the At Tanf garrison in southeastern Syria, according to the US-led military coalition fighting ISIS. "There was an incursion into the de-confliction zone," coalition spokesman US Army Col. Ryan Dillon told CNN, adding that after the pro-regime troops entered the zone, the US-led coalition used the pre-established de-confliction hotline and communicated the incursion to the Russians. Following that communication, the pro-regime forces withdrew. But the apparent successful use of the de-confliction channel comes amid new accusations by Russia that the US military is aiding ISIS."There was an incursion into the de-confliction zone," coalition spokesman US Army Col. Ryan Dillon saidRussia has alleged that the US military is aiding ISIS 
 Question:"We are hyper aware of what is inside At Tanf and near our forces" Dillon said, saying the coalition would go after them and kill _ fighters wherever they were.

ISIS