More rebel groups and ISIL fighters are infiltrating and taking territory.
The future of Syria's president, Bashar al-Assad, is increasingly in question.
Assad welcomed Iran's foreign minister on Wednesday. After signing a landmark nuclear deal with world powers, what is Javad Zarif doing in Damascus?
The visit by the major ally of the Syrian leadership follows increased diplomatic efforts; Russia, the United States and several Middle Eastern powers are all trying to find a way to end Syria's conflict.
Presenter: Shiulie Ghosh
Radwan Ziadeh: Executive Director, Syrian Center for Political and Strategic Studies.
Arron Reza Merat: Iran analyst for the Economist Intelligence Unit.
Christopher Swift, from the Center for National Security Law at the University of Virginia.