Doing rounds of Sunday talk shows on multiple news channels, Kerry said these samples were collected independently thorough an "appropriate chain of custody".
His remarks came a day after US President Barack Obama announced his decision of a military strike against Syria for use of chemical weapons against its own people in violation of the well-established international norms.
"We know that the regime ordered this attack, we know they prepared for it," Kerry told the 'State of the Union' on CNN.
"We know where the rockets came from. We know where they landed. We know the damage that was done afterwards. We've seen the horrific scenes all over the social media, and we have evidence of it in other ways, and we know that the regime tried to cover up afterwards, so the case is really an overwhelming case," he said in response to a question.
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"So this case is building and this case will build," the top American diplomat said.
Sarin is a man-made chemical warfare agent considered the most toxic. It attacks the nervous system.
During the interviews, Kerry defended the decision of Obama to seek a Congressional authorisation on a military strike against the Assad regime.