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
IS is now attracting women and whole families as well as young men - but will any return to carry out another 7/7?
Rain will be heavy across Scotland, parts of northern England and Wales tonight - rumbles of thunder are possible waking some of us up.
A report out tomorrow shows energy bills have been 5% higher than they should have been - costing Brits as much as £1.2 billion a year.