U.S. defense officials are accusing Iran of increased meddling in Syria, including efforts to bolster its flagging armed forces, who are weary after 18 months of war.
Defense Secretary Leon Panetta said Iran is building and training a militia to help President Bashar Assad's regime battle the rebel fighters trying to topple him.
The Iranian efforts, said Panetta, will only add to the killing going on in the country and "bolster a regime that we think ultimately is going to come down."
Sitting alongside Panetta at a Pentagon news conference Tuesday, Army Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, said the militia, which is generally made up of Syrian Shiite forces, is being used to take the pressure off the Syrian regime forces.
"Any army would be taxed with that kind of pace," Dempsey said. "They are having resupply problems, they are having morale problems, they are having the kind of wear and tear that would come of being in a fight for as long as they have."
Dempsey and Panetta voiced concerns about Iran's growing presence in Syria even as President Bashar Assad's regime steps up its aerial attacks against the rebel forces. Fierce fighting and attacks from warplanes and helicopter gunships have pushed the opposition forces back on key fronts, such as Aleppo.
Asked about military options for intervention in Syria, Dempsey said the U.S. has been in discussions with Jordan and Turkey about the possible need for a safe zone because the two countries neighboring Syria are seeing an influx of refugees fleeing the fighting.
"And with a safe haven would probably come some form of no-fly zone, but we're not planning anything unilaterally," Dempsey said.