State Department officials told lawmakers on Wednesday there is no "viable option" on the table for establishing a safe zone inside Syria for civilians and opposition rebels.
"We continue to look at this. We continue to study this. But there is no viable option on the table at this time," Ambassador Anne Patterson told the House Foreign Affairs Committee.
"The administration has looked at this over and over and over again, and there is no option on the table, nor recommended by the Department of Defense, that does not require a massive, massive amount of air support that would then detract from the effort against ISIL," she said, using another acronym for ISIS.
U.S. officials stressed that the administration is providing humanitarian support and pressing Russia to pressure ally Syrian President Bashar Assad to stop barrel bombing Syrian civilians and rebel fighters.
"[Secretary of State John KerryJohn KerryOvernight Defense: Obama defends Manning commutation after backlash | Mattis clears Senate panel Kerry: Trump can’t instantly undo Obama actions ‘All or nothing’ leaves us nothing MORE has] spoken to [Russian Foreign Minister Sergei Lavrov] virtually every day, also about our insistence that they exact some kind of restraint out of Assad for the support that they're giving, at least in the area of barrel bombing," said Victoria Nuland, assistant secretary of state for European and Eurasian Affairs.
Lawmakers from both sides of the aisle and some former senior Obama officials have expressed support for establishing no-fly or safe zones in Syria, where civilians could seek refugee and opposition rebels could regroup. They also argue that it could increase pressure for a political solution.
However, administration and some top military officials argue doing either would be difficult and be very resource-intensive.
They say that establishing a no-fly zone would include taking out Syrian air defenses and could bring the U.S. into conflict with Syria or Russia, which began an air campaign in Syria in September in support of the regime.
They also say establishing a safe-zone would require a ground forces to protect it, since it would be difficult to tell by air whether enemy forces were infiltrating it.
"It is also extremely difficult to patrol and to protect these safe zones on the ground. And that would require a very significant investment of ground forces of some sort. But the primary reason is the investment of air power," Patterson said.
Hillary ClintonHillary Rodham ClintonTrump country Dem takes risk by skipping swearing-in Five things to watch for in Mnuchin hearing Agriculture head backs Perez in DNC race MORE, the 2016 Democratic front-runner and President Obama's former secretary of state, made news last month when she announced she supported the creation of some kind of safe zone.
Former CIA Director David Petraeus and former Defense Secretary Robert Gates have also expressed support for establishing no-fly or safe zones.
Chris Harmer, a senior naval analyst for the The Institute for the Study of War, laid out different options in a Nov. 4 study for establishing no-fly zones, concluding that "it is possible" to establish a no-fly zone over parts of northern and southern Syria where Russia is not flying.
"It could result in humanitarian relief for the beleaguered Syrian civilian population and has the potential [to] change the framework of negotiations in favor of U.S. objectives," he said.