Iran's elite Revolutionary Guard Corps are actively training and assisting local militias inside Syria to fight alongside government troops that are waging a civil war against rebel forces looking to oust embattled President Bashar Assad.
"Iran is playing a larger role in Syria in many ways," Defense Secretary Leon Panetta told reporters at the Pentagon on Monday. "There's now an indication that they're trying to develop ... a militia within Syria to be able to fight on behalf of the [Assad] regime."
In Syria, Iran has continually sought to prop up the Assad regime, which Tehran sees as one of the country's key regional allies, since government troops began their violent crackdown against Syrian rebels 18 months ago.
Since then, Iranian influence in the country has only grown, to the dismay of the United States and other world powers seeking a peaceful resolution to the growing crisis in the country.
Earlier this month, members of the Free Syrian Army (FSA) captured and detained 48 Iranian nationals who were traveling in the country.
Rebel forces claim the Iranians were actually members of the Revolutionary Guard Corps. Tehran claims the men were religious pilgrims visiting holy sites in Syria.
Panetta declined to comment on whether the FSA hostages were in fact Iranian military during the briefing. But he did note the increasing Iranian presence on the ground in Syria was a "deep concern" to American military leaders.
"We do not think Iran ought to be playing that role at this moment in time [and] that it's dangerous ... it's adding to the killing that's going on in Syria," Panetta said.
Tehran's efforts "to bolster a regime that we think ultimately is going to come down" will only escalate the violence in Syria and result in thousands more wounded or dead, Panetta added.
Anti-Assad rebels have slowly been gaining ground in the northern part of the country, concentrating their forces in the city of Aleppo.
However, government troops have been mercilessly hammering rebel positions inside Aleppo over the past few weeks, zeroing in on anti-Assad forces with attack helicopters and fighter jets.
However, the intense fighting in and around Aleppo and elsewhere has taken its toll on Assad's forces, Chairman of the Joint Chiefs of Staff Gen. Martin Dempsey said at the same DOD briefing.
"The Syrian army has been fighting now for about 18 months or so. And any army would be taxed with that kind of pace," Dempsey said.
"They are having re-supply 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," the four-star general added.
Iran's attempts to create a pro-government militia could be one way to alleviate that mounting pressure on Syrian troops, Dempsey added.
News reports in May stated that Tehran attempted to smuggle a large arms shipment into Syria aboard an Iranian commercial airliner headed to Damascus.
The weapons were allegedly destined for Syrian government forces under the orders of senior commanders in Iran's Revolutionary Guard. In the past, Tehran has been known to use passenger airliners to move weapons and materiel to Hezbollah fighters in Lebanon.
Regardless of Tehran's motivations, Panetta made clear that all Iranian efforts to support the Assad regime and prolong the fighting in Syria need to stop.
"We've got to make sure that Iran does not exercise that kind of influence in Syria and try to determine the future of the Syrians, Syrian people," the Pentagon chief said. "The Syrian people ought to determine their future, not Iran."