A plan announced over the weekend for getting the bulk of Syria's chemical weapons out of the country in coming weeks has raised major concerns in Washington, because it involves transporting the weapons over roads that are battlegrounds in the country's civil war and loading them onto a ship that has no place to go.

The New York Times quoted intelligence analysts and Pentagon officials as saying the the shipments will be vulnerable to attack as they travel past the ruins of a war that has raged for two and a half years.

Asked what the backup plan would be if the chemical weapons components were attacked by opposition forces linked to Al Qaeda, or even elements of Assad's own forces, a senior American official said: "That's the problem - no one has attempted this before in a civil war, and no one is willing to put troops on the ground to protect this stuff, including us."

Another official noted that the choice now facing the United States and other nations was to "either leave the stuff in place and hope for the best, or account for it, get it out of there, and hope for the best. That's the 'least worst' option."