The weapon stockpiles in the country's main repositories are secure and accounted for, Defense Secretary Leon Panetta told reporters on Friday at the Pentagon.
"There has been intelligence that there have been some moves that have taken place. Where exactly that's taken place, we don't know," Panetta said.
Further, the DOD chief said he had no information on whether Damascus has fully accounted for all those weapons or if members of the Syrian resistance had captured pieces of those stockpiles.
"With regards to ... the movement of some of [the weapons] and whether or not [American intelligence] have been able to locate some of it, we just don't know."
U.S. military and intelligence officials are still grappling with the problem of missing weapons let loose after former Libyan dictator Moammar Gadhafi was removed from power and later killed by anti-government rebels in that country.
American intelligence officials have already picked up indications that some of those weapons, including shoulder-fired surface-to-air missiles, have made their way into the hands of terror groups operating in North Africa and the Mideast.
Assad's forces began mobilizing parts of their chemical weapons arsenal in July, as bitter fighting between government troops and anti-Assad forces spilled across the country.
At the time, concern on Capitol Hill mounted over the possibility of Assad ordering the use of those weapons against rebel forces.
“If Assad is transferring chemical weapons from secure sites to the battlefield, it significantly raises the risks that they will be used or that control over these weapons could be compromised," Sens. John McCain (R-Ariz.), Joe Lieberman (I-Conn.) and Lindsey Graham (R-S.C.) said in a July 13 joint statement.
"These are unacceptable risks for the United States and the entire international community, and they would threaten our vital national security interests," they said.
But Panetta sought to soothe such concerns during Friday's briefing.
The stockpile shifts being carried out by Assad's forces were intended to secure the weapons, not move them into position to be used against rebel forces.
"There has been some movement in order ... for the Syrian to better secure the chemicals," Panetta said. "And while there's been some limited movement, again, the major [weapon] sites ... still remain secure."