Secretary of State John Kerry said the UN inspectors could not tell the US anything it did not already know about the chemical weapons attack in Syria on August 21.
A intelligence report also said it was "highly unlikely" the Syrian opposition executed the attack.
More top news
Feeling colder with a biting, bitter windchill
A thoughtful teenager has taken Valentine's romance to a whole new level by buying 900 flowers and giving one to every girl in his school.
The group of Adelie penguins dwindled from 160,000 to 10,000 after an iceberg got stuck near their colony, scientists have found.