Any deal with Syria to hand over its chemical weapons in the middle of a chaotic civil war would be difficult for inspectors to enforce and destroying them would likely take years, US officials and experts caution.
Syria's strongest backer, Russia, proposed on Monday that Damascus save itself from a US military strike over its alleged use of chemical weapons by putting its stockpiles under international control.
The proposal was welcomed by Syria and seized upon by the secretary-general of the United Nations. US President Barack Obama said the offer was a potential breakthrough but had to be handled with scepticism.
Syria has never signed a global treaty banning the storage of chemical weapons and is believed to have large stocks of sarin, mustard gas and VX nerve agents. The actual use of chemical weapons is banned by a 1925 treaty to which Damascus is a signatory.
Accounting for Syria's chemical arms cache - believed to be spread over dozens of locations - would be difficult, as would be shielding arms inspectors from violence.
"This is a nice idea but tough to achieve," said one US official speaking on condition of anonymity.
"You're in the middle of a brutal civil war where the Syrian regime is massacring its own people. Does anyone think they're going to suddenly stop the killing to allow inspectors to secure and destroy all the chemical weapons?" the official said.
Amy Smithson, an expert on nuclear, biological and chemical weapons at the James Martin Center for Nonproliferation Studies in Washington, said a lack of hard data on Syria's chemical weapons inventory would complicate verification.
She pointed to years of cat-and-mouse manoeuvring between UN weapons inspectors and then-president Saddam Hussein in neighbouring Iraq as an example of what could happen in Syria.
"The Iraqis lied through their teeth. They did everything they could to hide these ultra-secret weapons programs," Smithson said.
"Libya also did not come completely clean when it forfeited their weapons of mass destruction program."
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