A[n unnamed] U.S. official confirmed Friday that the Syrian regime has been moving elements of its chemical weapons stockpile in recent days, an action that has U.S. officials both concerned and perplexed.

"We don't know why" they have begun moving chemical weapons from storage, the source said, refusing to speculate whether President Bashar Assad's regime could be preparing to use the weapons on the civilian uprising.

Asked whether there is concern that the weapons could fall into the hands of terrorists, the source said the United States still believes the chemical weapons are "secure" and under the control of the Assad regime.

Separately, Pentagon press secretary George Little said if the Assad regime were to use chemical weapons on civilians it would cross a "serious red line."

"We would, of course, caution them strongly against any intention to use those weapons," Little said.

While details of Syria's stockpile of chemical weapons remains a mystery, the United States believes the regime has significant quantities of sarin nerve agent, mustard gas and cyanide.

Opposition activists said Friday that more than 200 Syrians were massacred in a village in the Hama region on Thursday in what could prove to be the worst single incident of violence in 16 months of conflict.

Activists said the incident took place on the eve of the latest U.N. Security Council negotiations on a new resolution on Syria. The United States and its allies said it showed the need for tough action, but Russia ruled out accepting the latest draft.