Iran is working to form a pro-regime militia in Syria, US Defense Secretary Leon Panetta said Tuesday, warning that Tehran’s growing presence could only aggravate the situation on the ground.

“It is obvious that Iran has been playing a larger role in Syria in many ways,” Panetta said at a joint press conference with the chairman of the Joint Chiefs of Staff, General Martin Dempsey.

There is now evidence that Iran’s Revolutionary Guards are “trying to develop, trying to train a militia within Syria to be able to fight on behalf of the regime,” Panetta said.

“So we are seeing a growing presence by Iran and that is of deep concern to us. We do not think that Iran ought to play that role at this moment in time, that’s dangerous... it’s adding to the killing that’s going on in Syria.”

Panetta also called on Tehran to stay out of the conflict, saying: “Our hope is that Iran thinks better about how much they do want to get involved.”

“The Syrian people ought to determine their future, not Iran,” he added.

Most of the members of the apparent militia are Shiite, and some are Alawites like Syrian President Bashar Assad, Dempsey said, comparing the force to the Mahdi Army of anti-US Shiite cleric Moqtada Al-Sadr in Iraq.

Syria’s army has been weakened by desertions and defections within its top hierarchy, the US officials said.

“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, noting he expected that the Syrian military was experiencing resupply and morale problems.

“That’s why Iran is stepping in to form this militia, to take some of the pressure off of the Syrian military.”