US Vice President Joe Biden
US Vice President Joe BidenIsrael news photo: Flash 90

United States Vice President Joe Biden said Tuesday that there is "no doubt" that Syrian President Bashar Al-Assad was responsible for the August 21 chemical weapons attack near Damascus.

The comments came as the United States deliberates on how to respond to the chemical attack, which rebels said killed hundreds of people.

Speaking at the American Legion National convention in Houston, Texas, and quoted by CBS News, the vice president laid out the rationale behind his 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."

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.

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.

An aide to House Speaker John Boehner (R-Ohio) said on Monday that President Barack Obama was obligated to “consult with Congress on the options he sees as a viable response.”

As of early Tuesday afternoon, reported CBS News, 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."

Senior U.S. officials told NBC News on Tuesday that the United States may launch strikes against the Syrian regime “as early as Thursday.”