Biden: "No doubt" Assad responsible for Syria chemical weapons attack

Updated at 3:55 p.m. ET

As the Obama administration considers how to respond to the use of chemical weapons in Syria, Vice President Joe Biden said Tuesday that there is "no doubt" that Syrian President Bashar al Assad was responsible for the Aug. 21 chemical weapons attack near Damascus.

Speaking at the American Legion National convention in Houston, Texas, the vice president laid out the rationale behind that assertion.

"We know that the Syrian regime are the only ones who have the weapons," Biden said, "have used chemical weapons multiple times in the past, have the means of delivering those weapons, have been determined to wipe out exactly the places that were attacked by chemical weapons."

And instead of cooperating with international investigators, he continued, "the government has repeatedly shelled the sites of the attack and blocked the investigation for five days."

Biden said the administration's national security team has been in "close consultation" with their foreign counterparts. "Those who use chemical weapons against defenseless men, women and children should and must be held accountable," he said.

In the White House press briefing earlier Tuesday, White House spokesman Jay Carney said the United States must respond to the use of chemical weapons in Syria because "allowing the use of chemical weapons on a significant scale to take place without a response would represent a significant challenge or threat to the United States' security interests."

While Carney said "there must be a response," he noted that President Obama has yet to decide what course of action he'll take.

"A decision about the use of military force has not been made," he said. "His options are many, and they include a variety of options that are not limited to the use of force."

The potential for a military strike in Syria has triggered some concern in on Capitol Hill, where lawmakers are pointing out that the president cannot legally use military force without congressional approval. As of early Tuesday afternoon, nearly two dozen lawmakers had signed onto a letter calling on the president to get Congress' authorization before acting militarily.

"Engaging our military in Syria when no direct threat to the United States exists and without prior congressional authorization would violate the separation of powers that is clearly delineated in the Constitution," the letter says. "If you deem that military action in Syria is necessary, Congress can reconvene at your request. We stand ready to come back into session, consider the facts before us, and share the burden of decisions made regarding U.S. involvement in the quickly escalating Syrian conflict."