UNITED NATIONS — International inspectors are due to get their first look at Syria’s chemical weapons stockpiles within days, implementing a United Nations-backed plan to secure and destroy the deadly arsenal amid a civil war.

The Organization for the Prevention of Chemical Weapons plans to have inspections begin by Oct. 1 on a fast-tracked schedule to deny Syrian President Bashar al-Assad the use of his mustard gas and nerve agents. It envisions eliminating all Syria’s chemical weapons and related materials by mid-2014.

It’s the first time the Netherlands-based organization has undertaken such a task in a war zone. In addition to security, the plan faces hurdles that include U.S. and other countries’ doubts about Assad’s intentions and questions of where and how the weapons and related materials will be destroyed.

“Rightly, people have been concerned about whether Syria will follow through on the commitments that have been laid forth,” U.S. President Barack Obama told reporters yesterday at the White House. “And I think there are legitimate concerns as to how, technically, we’re going to be getting those chemical weapons out while there’s still fighting going on.”

Assad will quickly be tested by inspections, and the chemical weapons organization’s 41-nation Executive Council agreed to meet within 24 hours after any Syrian violations to consider referring the matter to the UN Security Council.

It’s unclear where and how Syria’s weapons and precursor chemicals will be destroyed. The executive council, which yesterday approved a directive on Syria, didn’t provide details. The council plans to set “destruction milestones” no later than Nov. 15, after a first wave of inspections.

“I think the council wants a better picture of Syria’s arsenal and stockpile locations before establishing a time line that it might need to walk back at a future date,” said James Lewis, communications director at the Center for Arms Control and Non-Proliferation, a Washington research group.

The OPCW is seeking contributions from member nations to help the organization and the Syrian government cover the “significant” costs, Director-General Ahmet Uzumcu said in a statement yesterday. “Never before has the OPCW faced a task of this magnitude and importance.”

While “no one underestimates the obstacles,” the timetable seems achievable, particularly given Russia’s backing and broad international support, said Joseph Cirincione, an arms-control analyst who’s president of the Ploughshares Fund, a San Francisco-based security foundation.

“The very good news is that it looks like much of this arsenal can be quickly destroyed,” he said in an interview.

The OPCW is breaking with past actions by sending inspectors into a war zone. The group suspended activities in Libya when the civil war there broke out in February 2011.

“Because Syria is in the midst of civil war, there are many risk factors that have not been present in past cases of chemical weapons destruction such as in Libya or Iraq,” according to a Sept. 12 report by the Congressional Research Service.

The U.S. blames the Assad regime for an Aug. 21 attack using sarin gas, citing more than 1,400 deaths, a quarter of them children. Assad denies responsibility and, echoed by Russia, blames “terrorist” rebels despite evidence from a UN team implicating regime forces. Obama threatened military strikes before backing off once U.S. Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov reached a deal Sept. 14 in Geneva to eliminate Assad’s chemical weapons.

Assad agreed to join the Chemical Weapons Convention and give up his arsenal. It was the first time that Syria acknowledged it has chemical munitions, providing an initial inventory as required to the OPCW, the international body that implements the 1997 Chemical Weapons Convention banning such munitions.

Syria is believed to have one of the world’s largest such arsenals, including mustard gas, which had horrific consequences during trench warfare in World War I, and more advanced sarin and VX nerve agents, lethal offshoots of insecticides. Its program is “large, complex, and geographically dispersed,” according to the U.S. intelligence community’s 2013 Worldwide Threat Assessment.

The U.S. has attempted to monitor Syria’s chemical weapons during the civil war by focusing surveillance on suspected stockpile sites and movements, according to U.S. officials who weren’t authorized to discuss intelligence matters.

The lack of firm knowledge about Assad’s weapons — which a UN official has said are under the control of elite military units led by his brother Maher — was reflected in the Geneva negotiations: Kerry and Lavrov could do no better than agree on an estimate of 1,000 metric tons of chemical weapons and precursor chemicals.

Syria has “thousands of munitions” that can be used to deliver chemical weapons, the White House said in an Aug. 30 statement. Those range from bombs and artillery rockets to Scud missiles.

Syria is “determined to go forward” in giving up chemical weapons, Syrian Foreign Minister Walid al-Muallem told Al Jazeera television yesterday at the United Nations.

The OPCW Executive Council said Syria must provide a more detailed inventory by Oct. 4. Among other things, that accounting will show whether the regime has munitions that match those used in the Aug. 21 attack.

The OPCW will attempt to verify that the information Syria provides is accurate and that Assad isn’t copying the late Iraqi leader Saddam Hussein, who played hide-and-seek with UN weapons inspectors during the 1990s before he eliminated his chemical and biological weapons.

The OPCW directed inspectors to visit all of Syria’s declared chemical weapons facilities in the next 30 days. Beyond those, the OPCW demands that the secretive Assad regime permit “immediate and unfettered” inspections at “any and all sites,” including those based on information provided by other nations such as the U.S.

Syria must provide access “to any and all sites and any and all people” sought by inspectors, Kerry said at the UN Security Council yesterday, as the council voted unanimously to back the OPCW plan.

To prevent delay and obstruction by Assad, the OPCW executive council said that only the group’s director-general can block an inspection, in effect preventing Syria from using the time-consuming challenge process permitted other nations.

As called for in the Sept. 14 Geneva agreement by Kerry and Lavrov, the OPCW set a November target date for completing the destruction of all chemical weapons production and mixing or filling equipment, effectively capping nerve gas stocks.

The Kerry-Lavrov accord called for the the removal of the “largest amounts of weapons feasible, under OPCW supervision, and their destruction outside Syria.” The possibility that Russia would transfer the chemicals to its destruction facilities was ruled out Sept. 26 by Deputy Foreign Minister Sergey Ryabkov, according to Russian state broadcaster RT.

“There’s no doubt, we won’t do it,” Ryabkov said, adding that the materials and equipment should be destroyed in Syria.

Chemical weapons can be destroyed by neutralization or incineration, which generally requires building special facilities to reduce the risk of accidental contamination and danger to nearby populations.

About a third of Syria’s weapons are thought to be mustard gas, which can be chemically neutralized, and the nerve-agent precursor chemicals don’t post a threat until they’re mixed, said Cirincione. Destroying stocks of VX and sarin by incineration is the most difficult.

By putting the weapons under monitoring, destroying mixing equipment and removing precursor chemicals, “you’ve effectively destroyed the chemical arsenal, even if some of it takes a little longer” to eliminate, said Cirincione.

The OPCW’s timetable for Syria is a very short compared to others. Both the U.S. and Russia have stockpiles not yet destroyed. Albania got attention in 2007 when it completed the destruction of about 16 metric tons of Cold War-vintage chemical arms, 10 years after it joined the Chemical Weapons Convention.

Under the convention, countries are responsible for paying destruction costs. Assad, in a Sept. 18 Fox News interview, said he’s been told that it may take about a year and cost as much as $1 billion to destroy the chemical arsenal, indicating others would need to help cover the costs.

U.K. Foreign Secretary William Hague yesterday said his country will make an initial contribution of $3 million to the OPCW trust fund and urged other countries to donate to the Syria effort, which will be expensive.

The OPCW council, without providing a cost estimate, appealed for financial contributions from nations “in a position to do so,” and authorized hiring an unspecified number of inspectors, technical experts and other personnel to meet new staffing needs.