The White House has warned the Syrian government that it will be "held accountable" for safeguarding any chemical weapons in its possession.
The warning comes amidst reports that Assad's regime have been quietly shifting some chemical weapons from storage sites.
The Syrian government denies the reports. Syria's undeclared stockpile is believed to be the largest of its kind in the Middle East, and is said to include sarin nerve agent, mustard gas and cyanide. White House spokesman Josh Earnest said:
There are certain responsibilities that go along with the handling and storage and security of those chemical weapons. We believe that the individuals who are responsible for living up to those challenges should do so and will be held accountable for doing so
More top news
The Foreign Secretary described Jeremy Corbyn as a "mugwump" - but what does that obscure word mean?
Readers are shunning e-books in favour of their traditional counterparts, which sold last year at their highest level since 2012.
Glaucoma is the biggest cause of permanent blindness and affects 60 million people around the world - a tenth of whom are completely blind.