While hundreds of U.S. bombing runs and missile strikes have put Islamic State forces on the defensive in Iraq, they have not had the same kind of impact in Syria. Instead, Islamic State fighters have enlarged their hold on Syria since the U.S. started hitting the group’s Syrian strongholds in September, according to the new estimates by the Defense Department and independent analysts.

Islamic State’s ability to grab more territory in Syria is one outgrowth of the U.S. decision to focus its military efforts on Iraq, where the militant group has seized major parts of the country and declared them part of a new Islamic Caliphate. The U.S.-led military effort has pushed Islamic State forces out of some key battlegrounds in Iraq.

But Syria still serves as a haven for Islamic State fighters, also known in the West by the acronyms ISIS and ISIL.

“Certainly ISIS has been able to expand in Syria, but that’s not our main objective,” said one senior defense official. “I wouldn’t call Syria a safe haven for ISIL, but it is a place where it’s easier for them to organize, plan and seek shelter than it is in Iraq.”