After Russia intervened in the dispute over chemical weapons in Syria and averted a Western strike on its client Bashar al-Assad, the matter has largely disappeared from the headlines. Late last month, however, rebels in Syria accused Assad of launching new chemical-weapons attacks on civilian populations. News reports of casualties have been accelerating, such as in this AP video:

Today, the Washington Post reports that Assad has retained 27 tons of sarin ingredients, hoping to use that as leverage:

The months-long effort to dismantle Syria’s chemical weapons program has ground to a halt because Syria is holding on to 27 tons of sarin precursor chemicals as leverage in a dispute with the international community over the future of facilities used to store the deadly agents, according to U.S. officials.

Having turned over all but an estimated 8 percent of its chemical arsenal to the Organisation for the Prohibition of Chemical Weapons, Damascus missed a deadline Sunday to relinquish the remnants of its arsenal, which are stored in 16 containers in Damascus, U.S. officials said.

The OPCW is insisting that a network of tunnels and buildings that were used to store the weapons must be destroyed. The government of Syrian President Bashar al-Assad has argued that the facilities should be repurposed.

“They’re just stalling for time to hold on to some of these facilities,” said a U.S. official familiar with the matter who would discuss the issue only on the condition of anonymity. The official said he expects that Syria will ultimately give up the material.

In part, they’ll give it up because they have an alternative — chlorine. They’re using it now, which suggests that they may be doing so to increase their leverage over the status of their current facilities, too. The international community can’t do much about chlorine, and so far they’re not even willing to concede that Assad is actually using it:

A senior U.S. intelligence official said U.S. intelligence agencies have little doubt that the attack was carried out by the government and that the toxic substance that led victims to choke was “likely chlorine.”

The use of chlorine as a weapon in Syria, if confirmed, would pose a dilemma for Washington, since it could not conceivably seek to rid Syria of a widely available chemical with numerous legitimate uses.

“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.”

Another analyst quoted by the Post called the use of chlorine gas “puzzling,” because it has a very limited military value. But Assad isn’t using it for its tactical value; he’s using it as a weapon of terror. He wants to flush the rebels out from civilian areas where they get support. This isn’t difficult to figure out, but the twist here is that the rebels in many cases are terrorist groups too, who hide in civilian areas to keep from being attacked frontally by military units. Given half a chance, they’d use chlorine gas, and worse — which is another good reason to get the sarin components before the rebels get their hands on them.

The UN may investigate the use of chlorine, but, er … don’t expect much more than a strongly-worded memo, especially with Russia and its veto staying at Assad’s disposal.