Leon Panetta
Leon Panetta Reuters

Former U.S. Defense Secretary Leon Panetta is criticizing President Barack Obama for leaning toward, then deciding against military action against Syria for its use of chemical weapons.

"By failing to respond, it sent the wrong message to the world," Panetta says in a new book, an early copy of which was seen by The Associated Press (AP) over the weekend.

In August 2012, Obama said the U.S. would reconsider its opposition to military involvement in the Syrian civil war if President Bashar Al-Assad deployed or used chemical or biological weapons.

"That's a red line for us," the president said. "There would be enormous consequences if we start seeing movement on the chemical weapons front, or the use of chemical weapons. That would change my calculations significantly."

But even after Assad used chemical weapons, killing hundreds of Syrian civilians, Obama planned a Rose Garden address in which it was widely expected to announce airstrikes against Assad, Obama instead said he would consult with Congress.

"President Obama vacillated, first indicating that he was prepared to order some strikes, then retreating and agreeing to submit the matter to Congress," according to an early copy of Panetta’s book quoted by AP.

"The latter was, as he well knew, an almost certain way to scotch any action. By mid-2013, a majority of Congress could not agree on what day of the week it was, much less a resolution authorizing the use of American force in the Middle East,” Panetta writes in the book.

"The result, I felt, was a blow to American credibility. When the president as commander in chief draws a red line, it is critical that he act if the line is crossed. ... Assad's action clearly defied President Obama's warning," he writes.

Panetta's book, "Worthy Fights," is scheduled for release next week.

Obama’s decision not to attack Syria ultimately led to its signing up to an international plan, backed by Washington and Moscow, to destroy its chemical stockpile.

Obama announced in August that Syria's declared chemical weapons stockpile was eliminated, declaring this an important achievement against the spread of dangerous weapons of mass destruction.

Even as the operation to destroy the chemical weapons was going on, there have been reports by local activists that President Bashar Al-Assad’s regime had used chlorine weapons against civilians.

Syria has emphatically denied that it had carried out chlorine gas attacks against civilians, but the Organization for the Prohibition of Chemical Weapons has confirmed that chlorine gas was used in attacks in northern Syria, saying it had found "compelling confirmation" of the use of chlorine.