The shipments of Russian-built anti-ship missiles to Assad's forces was "an unfortunate decision that will embolden the regime," Chairman of the Joint Chiefs of Staff Gen. Martin Dempsey said Friday.
Those weapons and Moscow's continued support of Assad's bloody offensive against Syrian rebels in the three-year-old civil war, could create a false sense of security among government forces, Dempsey told reporters during a press briefing at the Pentagon.
That sense of security, Dempsey added, could prompt Assad's force into making a "miscalculation" in their efforts to quash rebel forces, such as using chemical weapons against the opposition.
That action, or similar actions, would all but guarantee the civil war boiling over into a regional conflict.
The suspected use of chemical weapons by the Assad regime against rebel forces crossed a "red line" set by President Obama and further fueled congressional calls for U.S. action.
But the possibility of the war spilling over into neighboring countries, like Jordan or Turkey, is the biggest threat facing the American-led diplomatic efforts to force Assad from power, Defense Secretary Chuck Hagel said at the same press conference.
That said, the "escalation of weaponry" in Syria is only accelerating the possibility of a regional conflict breaking out, Hagel noted.
Despite that threat, neither Hagel nor Dempsey would comment on whether the recent Russian arms shipments, or possible shipments of S-300 surface-to-air missiles to Assad's forces, would force Washington's hand to arm the opposition.
Both Pentagon leaders reiterated the Obama administration's stance that all options, including military action, are still being considered to end the conflict.
Dempsey admitted the Pentagon has yet to draft up contingency plans to prevent future Russian arms shipments from heading into Syria.
Defense Department leaders are focusing on the current military threats coming from the Assad regime, from their possible use of chemical weapons to the country's advanced anti-aircraft weaponry.
"We do not have options, in any way" to prevent the future deliveries of advanced weaponry from Russia, according to Dempsey.
However, he noted the department would be able to tackle that issue, should the request for those plans be made by the White House.
Last Friday, Foreign Minister Sergei Lavrov vowed to block any new sales to Assad's forces but also promised to deliver on previous sales to the regime.
"Russia already sold them [weapons] a long time ago. It has signed the contracts and is completing deliveries, in line with the agreed contracts," including previously agreed to deliveries of S-300 long-range, surface-to-air missile systems, Lavrov said at the time.