U.S. officials claim that the Syrian government is holding on to its remaining stockpile of chemical weapons in an attempt to gain leverage in negotiations over the future of the system of tunnels and buildings used as storage, according to a published report. 

The Washington Post reported late Wednesday that Damascus is keeping 27 tons of chemicals that are precursors to sarin gas in 16 containers in the capital. The paper reported that the deadline to relinquish the remainder of its arsenal to the Organization for the Prohibition of Chemical Weapons (OPCW), the U.N.'s watchdog, passed April 27. 

The OPCW is demanding that the Syrian government destroy the storage and conveyance network, while the government of Bashar al-Assad wants the facilities to repurposed, though it is not clear what their use would be.

The impasse has put the actions of the Syrian government under scrutiny, as have reports that Syrian forces have begun using chemicals in so-called barrel bombs that have struck several towns in the rebel-held northwest of the country. The Daily Telegraph reported Wednesday that independent tests showed high levels of chlorine in the area of strikes on the village of Kafir Zeita, which was hit three times over the course of one week. 

The Post reported, citing a U.S. intelligence official, that U.S. intelligence agencies have little doubt the strikes this month were carried out by Assad's forces, who likely used chlorine. The Syrian government has blamed rebel forces for carrying out the attack.

Despite the agencies' conclusions, U.S. officials are reportedly reluctant to raise the issue of the latest attacks until the remaining stockpiles of sarin and other agents are removed. 

"There’s reluctance to call attention to it because there’s not much we can do about it," a senior U.S. official said. "You can’t ask a country to get rid of all its chlorine."

Damascus has until June 30 to abandon and destroy its entire arsenal of chemical weapons. 

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