Secretary of State John Kerry says the U.S. knows based on intelligence that the Syrian regime carefully prepared for days to launch a chemical weapons attack.
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Kerry says Syrian regime personnel were on the ground for three days beforehand, making preparations.
He says regime elements were told to prepare by putting on gas masks.
Kerry says the U.S. also knows where the rockets were launched from. He says the rockets came from regime-controlled areas.
Kerry also says a senior regime official confirmed that the weapons were used and was afraid it would be discovered.
The U.S. has released a public report on intelligence gathered about last week's deadly attack. President Barack Obama is preparing for a possible military strike in response.