Hair and blood samples from Syria tested positive for the nerve agent sarin, US Secretary of State John Kerry said in television interviews as he sought to build the case for Congress to authorise a military strike.
Bashar al-Assad now joins the list of Adolf Hitler and Saddam Hussein.
"It has tested positive for signatures of sarin," Kerry said today on CNN. "So each day that goes by, this case is even stronger."
Barack Obama speaks about Syria next to Vice President Joe Biden at the Rose Garden of the White House on Saturday. Photo: Reuters
The disclosure of potential forensic evidence in the August 21 attack, which Kerry said was obtained by the US from first responders in east Damascus, came one day after President Barack Obama slowed the path toward a military strike by saying he will seek authorisation from Congress.
Originally conceived as a pesticide, sarin was developed by Nazi scientists in 1938. It was used by Iraqi dictator Saddam Hussein’s regime to gas thousands of Kurds in the northern town of Halabja in 1988 and cult also used the odorless, paralysing agent in two attacks in Japan in the 1990s. It cripples the respiratory centre of the central nervous system and paralyses the lungs, resulting in death by suffocation. A single, pin-prick sized droplet can kill a human and is 26 times more deadly than cyanide gas, according to the World Health Organisation.
Kerry, who conveyed a sense of urgency in laying out the case for a military strike two days ago in a public address at the State Department, dismissed suggestions that his effort was undermined by Obama's surprise decision to go to Congress.
"I did not advocate that the response had to be swift," he said in an interview on CBS's Face the Nation program. "There was an appropriate, deliberate process."
Appearing on all five Sunday network news programs, Kerry made the case for why Congress should approve intervention in a Syrian conflict that has lasted more than two years and resulted in more than 100,000 deaths.
"Bashar al-Assad now joins the list of Adolf Hitler and Saddam Hussein" who have used chemical weapons in times of war, Kerry said on NBC's Meet the Press program. "This is of great consequence to Israel, to Jordan, to Turkey, to the region, and to all of us who care about enforcing the international norm with respect to chemical weapons."
Kerry, who opposed the Iraq war while running unsuccessfully for president in 2004, has become Obama's most visible advocate for punishing the Syrian regime for using chemical weapons. The secretary of state raised expectations for an imminent response when he said on August 30 that the US had amassed "clear" and "compelling" evidence that chemical weapons were used.
The US says the August 21 attack by the Syrian regime in a Damascus suburb with chemical weapons killed 1429 people, including at least 426 children. The Syrian government has denied using chemical weapons, saying elements of the opposition were responsible.
Obama made the decision to seek congressional authorisation late on August 30 as he walked around the South Lawn of the White House and talked for 45 minutes with White House Chief of Staff Denis McDonough, according to an administration official who asked not to be identified.
The President didn't consult Kerry or other cabinet members such as Defense Secretary Chuck Hagel before the decision was reached, the official said.
Kerry said today that approval from Congress would strengthen Obama's hand in building a coalition to punish the Assad regime.
"Our democracy is stronger when we respect the right of Congress to also weigh in on this," he said on CNN.
Kerry said a decision by Congress to oppose military action wouldn't prevent the President from launching a strike.
"He has the right to do that no matter what Congress does," Kerry said on CNN.
Even so, he said, "We don't contemplate that the Congress is going to vote 'no'. This case grows powerful and more powerful by the day."
A US intelligence report released last week concluded with "high confidence" that the Assad government carried out the August 21 attack. Syria has a stockpile of chemical agents – including mustard, sarin and VX – and "thousands" of munitions to deliver them, it said.
Lawmakers offered mixed predictions today on whether Congress will authorise military action.
"If the vote were today, I think it would be a 'no' vote," said Representative Peter King, a New York Republican who sits on the House intelligence and Homeland Security committees.
"The President has not made the case," King said on Fox News Sunday. "When they see the President being so weak and vacillating, many members of Congress will vote no."
Representative Mike Rogers, a Michigan Republican who heads the House intelligence committee, backed Obama's decision to seek a vote in Congress.
"At the end of the day, Congress will rise to the occasion," he said on CNN. "This is a national security issue. This isn't about, you know, Barack Obama versus the Congress. This isn't about Republicans versus Democrats. This has a very important worldwide reach in this decision."
More than 100 of the 435 lawmakers in the US House of Representatives, including 18 of Obama's fellow Democrats, signed a letter last week saying Syria doesn't pose a direct threat to the US and calling on him to seek congressional approval before any military action.
Republican Senators John McCain of Arizona and Lindsey Graham of South Carolina, who have long urged a more aggressive US role in Syria, have said Obama wasn't planning to do enough.
"We have to have a plan," McCain said on CBS. "It has to be a strategy. It can't just be, in my view, pinprick cruise missiles."
He said the best way to eliminate the danger of Assad using chemical weapons "would be the threat of his removal from power." Obama has said a military strike would be limited and wouldn't include a goal of regime change.
Kerry said he spoke with McCain and Graham as recently as yesterday.
"I am convinced that we can find common ground here with them and others so that they're convinced that the strategy that is in place will, in fact, help the opposition," he told ABC.
The US has warships on standby in the region that could launch Tomahawk cruise missiles. A Navy amphibious ship, the USS San Antonio, arrived in the eastern Mediterranean yesterday, joining five destroyers. The San Antonio, which typically carries about 300 Marines, could be used to evacuate US personnel from embassies in the Middle East.
Senator James Inhofe of Oklahoma, the top Republican on the Senate Armed Services Committee, chided Kerry today for saying a military strike would be limited.
"We all know that isn't going to be the case," Inhofe said on Fox. "It's going to be something that could be long and last a long period of time."
Richard Haass, president of the Council on Foreign Relations, a New York-based policy group, said the decision to seek a vote in Congress threatens to weaken the US position.
"It's important to do the strike," Haass told CNN. "We've made it more difficult for ourselves with the delay and now with the need for congressional authorisation. We've raised all sorts of questions about our reliability. We've raised questions about our predictability."
Vali Nasr, a Middle East scholar who is dean of the Johns Hopkins School of Advanced International Studies in Washington, said Obama has been hamstrung in trying to deter Assad by US reluctance to intervene in Syria's civil war.
"The critical deterrence is American decisiveness and commitment to the region," Nasr said on ABC. "And unless and until that's there, I don't think we are either impressing our allies or we're really threatening Assad."