Samples collected by first responders after the Aug. 21 chemical attack in a Damascus suburb have tested positive for the Sarin nerve agent, US Secretary of State John Kerry told US media as he sought build support for a military strike.

Kerry made his comments as part of a series of nine TV appearances to persuade the US public opinion of the need for military retaliation on Syria, following Saturday’s announcement by Barack Obama that he will seek approval for the use of force in Congress.



“In the last 24 hours, we have learned through samples that were provided to the US that have now been tested from first responders in east Damascus and hair samples and blood samples have tested positive for signatures of sarin," Kerry said on NBC's Meet The Press.



In a later appearance on CNN, Kerry said that the evidence, which was gathered independently of the UN, strengthened Obama's call for military action against the regime of President Bashar Assad, which the US accuses of being responsible for the chemical weapons attack.



"Each day that goes by, this case is even stronger," Kerry said, calling the case “overwhelming.”



Sarin is a man-made chemical warfare agent, considered the most toxic and fast-acting of its kind. The odorless, colorless nerve agent interferes with an enzyme called acetylcholinesterase that controls nerve signals to the muscles.



The US lawmakers are to return from recess on September 9. Kerry said he believed there are “good people in the Congress” who would support intervention.



In his interviews, Kerry avoided answering the question whether Obama would still act if the Congress voted against strikes on the Syrian targets.



Meanwhile, in an interview with ABC, Kerry expressed the hope that Russia would realize that Assad crossed the line by using chemical weapons against civilians, and join the US in their effort to hold the Syrian regime accountable.The head of the Foreign Affairs Committee of the Russian Duma, Aleksey Pushkov, believes that Kerry’s claims of discovered sarin traces doesn’t in any way prove that the chemical weapons were used by the Syrian government.Pushkov wrote on his Twitter page.

Russia has been calling for a full investigation into the allegations surrounding the Aug. 21 attack which reportedly killed hundreds of people. On Saturday, Russian President Vladimir Putin urged Washington to present its evidence to the UN Security Council before beginning the attack, saying doing otherwise would be “a violation of international law.”



Putin labeled as “utter nonsense” the idea that the Syrian government would use chemical weapons on its own people when UN inspectors were in Damascus, calling the whole affair a “provocation” by Syrian rebels hoping to embroil Western powers in the conflict.



Meanwhile, the samples that UN investigators gathered at the site of the attack near Damascus are yet to be sent to European laboratories, UN spokesman Martin Nesirky said.



According to Nesirky, “two Syrian officials” will be monitoring the testing to ensure transparency.



Earlier, UN Secretary General Ban Ki-moon said it may be two weeks before the final results of the analysis are ready.