The Syrian regime threatened to use chemical and biological weapons in the case of an external attack yesterday, in what appeared to be a chilling warning to Western and Arab nations pushing for intervention in the country's bloody civil war.

The comments by a foreign ministry spokesman, Jihad Makdissi, were the first public admission by the Syrian government that it possesses such weapons of mass destruction. Mr Makdissi stressed that such weaponry would not be used against the Syrian people.

"All of these types of weapons are in storage and under security and the direct supervision of the Syrian armed forces and will never be used unless Syria is exposed to external aggression," he said.

The Syrian regime is believed to be in possession of large stockpiles of sarin, other nerve agents, and mustard gas. Western officials have voiced concern over their safety and potential deployment in recent weeks.

The Foreign Secretary, William Hague, described the threat to use them as "unacceptable".

"This is typical of the complete illusion of this regime, that they are the victims of external aggression," Mr Hague said.