The Pentagon and an international monitoring organization have said that Gaddafi’s remaining stockpiles are secure. But more than 11 tons of mustard gas is known to be accumulated in a country that suddenly lacks a strong central authority and where weapons are fast proliferating. Libyan rebels say they are concerned that Gaddafi holdouts could have access to the mustard gas and could use it in a last-ditch effort to halt advances by the opposition.

“It hasn’t happened yet, but it’s not beyond Gaddafi,” said Mohammed Benrasali, a senior member of Libya’s civilian stabilization team…

U.S. officials were skeptical Wednesday about assertions that Gaddafi loyalists were preparing to use chemical weapons — or even possessed them. One senior official, who spoke on the condition of anonymity to discuss U.S. intelligence assessments, said Gaddafi’s remaining stocks of mustard agent are thought to be secure. The chemicals, the official said, are stored in bulk containers and are difficult to use.