Speaking in Belgrade, Ban Ki-moon, the United Nations secretary general, has said he is "very concerned Syria may be tempted to use chemical weapons".

In Washington, the United States issued warnings to the Assad government about the possibility of utilising Damascus' stockpile of chemical and biological weapons.

"They should not think one iota about using chemical weapons," George Little, Pentagon press secretary, told reporters.

We have been very strong in our statements inside the US government on the
prospective use of chemical weapons and it would be entirely unacceptable.