WASHINGTON — U.S. and allied intelligence have detected Syrian movement of chemical weapons components in recent days, a senior U.S. defense official said today, as the Obama administration strongly warned the Assad regime against using them.

A senior defense official said intelligence officials have detected activity around more than one of Syria’s chemical weapons sites in the last week.

Secretary of State Hillary Rodham Clinton, in Prague for meetings with Czech officials, reiterated President Barack Obama’s declaration that Syrian action on chemical weapons was a “red line” for the United States that would prompt action.

“We have made our views very clear: This is a red line for the United States,” Clinton told reporters.

“I’m not going to telegraph in any specifics what we would do in the event of credible evidence that the Assad regime has resorted to using chemical weapons against their own people. But suffice it to say, we are certainly planning to take action if that eventuality were to occur.”

Syria said today it would not use chemical weapons against its own people. The Ministry of Foreign Affairs said Syria “would not use chemical weapons — if there are any — against its own people under any circumstances.”

Syria has been careful never to confirm that it has any chemical weapons.