Even as President Bashar al-Assad of Syria is proclaiming battlefield momentum against the insurgency with the help of his Hezbollah ally, he appears to be facing a new threat: a rapidly weakening currency that has unnerved many Syrians.

The currency, the Syrian pound, fell about 30 percent in value against the dollar over the weekend, partly on news that the United States intended to arm some elements of the rebellion seeking to topple Mr. Assad.

Money traders and economists said the plunge might have been accelerated by the apparent unwillingness — or inability — of Syria’s Central Bank to halt it by buying pounds with dollars or euros, suggesting the government’s supply of foreign exchange reserves is running low.

The Central Bank governor, Adib Mayalah, announced Tuesday that to help stabilize the pound, Syria would tap into a $1 billion credit line provided by Iran. That appeared to be helping on Wednesday. But the effects of that aid are considered temporary at best, as Iran is facing its own severe financial constraints.