WASHINGTON (AP) -- 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.
Kerry says Syrian regime personnel were at the site of the attack 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 chemical attack this month in Syria killed 1,429 people, including at least 426 children, Kerry says.
Those numbers are significantly higher than what Syrian activists and aid workers have reported from Syria.
The death toll is contained in a declassified intelligence assessment released by the Obama administration at the same time Kerry was speaking about the Syrian attack.
The administration blames the Syrian regime for the deaths.
The U.S. is releasing a public report on intelligence gathered about last week's deadly attack. President Barack Obama is preparing for a possible military strike in response.