Earlier this week insurgents captured the Brigade 61 base at Tal al-Jabiyah, the largest regime position between Quneitra and Daraa in southern Syria.

In the celebrations, however, another story was lost: in late February, the US had tried to block the insurgent advance.

See Did US Halt Insurgent Advance on Chemical Weapons Base?

Why? And why were opposition fighters allowed to proceed two months later — or did they defy the Americans as well as defeat Assad forces?

Insurgents had shelled Tal al-Jabiyah for months, and in February they launched a ground assault. By February 25, they were on the verge of taking a fortified bunker in the complex.

At that point — according to sources “familiar with the situation” — US, European, and Arab military and intelligence officers warned the insurgents that they must halt.

Based in the Military Operations Command in the Jordanian capital Amman, the foreign officers said Israeli jets were on standby to bomb the bunker, less than 8 kilometers (5 miles) from the Israeli border.

The Command’s officials said only that the bunker’s munitions were “strategic weapons”. A defector from the compound said they included the nerve agent sarin, even though Tal al-Jabiyah was not included on the list of chemical weapons sites which the Assad regime was forced to declare to the United Nations after its attacks on Damascus suburbs last August.

On February 25, the foreign officers used an intermediary to tell the commander of the Islamist faction Jabhat Al Nusra in Daraa Province: hand over any captured weapons or an Israeli airstrike would destroy the compound.

The commander agreed, but the officers were still not satisfied. Four hours later, insurgents were told to expect an “international operation” against the bunker. All weapons supplies to the advancing fighters were halted.

The opposition fighters were forced to halt, and the Syrian military reinforced the complex.

So what happened between February 25 and this week?

Were there ever “strategic weapons” at Tal al-Jabiyah, including chemical stocks? Did they disappear, effectively allowing the insurgents to resume their advance? Or did opposition fighters proceed despite the resistance of foreign backers?