International inspectors have destroyed in four weeks nearly all the equipment used by Syria to prepare munitions for chemical warfare, dramatically reducing the country’s ability to launch a large-scale attack similar to the one that killed more than 1,000 Syrians in August, U.S. and European officials said.

The organization in charge of the inspections said Monday that its teams had visited all but two of the 23 chemical-weapons sites declared by Syria, in some cases smashing with hammers the machines used to fill chemical warheads with sarin and other lethal toxins.

The two remaining sites, located in areas contested by rebel fighters, are believed to be storage facilities and it is unknown what kind of production equipment, if any, exists there. But a European diplomat familiar with the inspection effort said the bulk of the equipment used by Syria to prepare its chemical munitions appears to have been “rendered inoperable.”

Obama administration officials were more reserved in their assessment but said they are cautiously optimistic that Syria’s entire arsenal could be eliminated by the deadline of early summer. A plan developed jointly with Russia called for prioritizing the destruction of Syria’s chemical-weapons production equipment, a task that was to be completed by Nov. 1.

“The first milestone will be met,” said a senior State Department official, speaking on the condition of anonymity because of diplomatic sensitivities surrounding the effort. “The inspectors are on the cusp of destroying all the mixing equipment.”

U.N. humanitarian aid chief Valerie Amos is calling for stronger action to increase aid to Syria, where she says conditions are going from “very bad” to worse. (The Washington Post)

Jean Pascal Zanders, a former researcher for the European Union Institute for Security Studies, said the reports suggest that Syria’s capacity to make more chemical munitions “is fairly reduced, if not entirely destroyed.” The overwhelming majority of Syria’s stockpile consists of bulk precursor liquids that must be mechanically mixed and injected into bombs or missile warheads, he said.

Although Damascus is believed to possess a small number of battlefield-ready munitions, Syria “probably doesn’t have the ability to wage chemical warfare” on the scale that would have been possible a month ago, said Zanders, who runs “The Trench,” a blog about nonproliferation.

Syria agreed to surrender its stockpile under a Russia-brokered accord after the Obama administration threatened to launch a military strike as punishment for allegedly attacking two Damascus suburbs with sarin on Aug. 21.

The Organization for the Prohibition of Chemical Weapons began its inspections on Oct. 2, focusing on 23 sites that Syria identified as associated with its chemical-weapons program. Syria on Saturday submitted a longer declaration that described its toxic arsenal and production facilities in detail, said Western diplomats familiar with the confidential document.

U.S. officials have been seeking to resolve discrepancies between Syria’s declaration and Western intelligence estimates of the number of chemical-weapons sites. It was unclear whether the gap is because of Syrian omissions or differences in how clustered facilities are counted, the State Department official said.

The official acknowledged that significant challenges remain, including how the teams will eliminate tons of precursor chemicals stored in several locations throughout the country. Since Norway publicly declined to accept the chemicals earlier this month, negotiations have begun with at least one other country to host a decontamination facility on its soil.

Despite the inspectors’ inability so far to reach two of Syria’s declared chemical sites, the Syrian government has cooperated with inspection teams, providing access as well as security, the State Department official said.