The United Kingdom and the United States said on Wednesday they would suspend their aid to the Syrian opposition after a weapons depot near the Turkish border had fallen into the hands of Islamists. Brigadier General Salim Idris, the Free Syrian Army’s commander, reportedly fled to Turkey.

His group, which is believed to be moderate and supported by Western nations that sympathize with the rebellion against the regime of President Bashar al-Assad, said it had asked other Islamist militants to help it retake the storage facility from insurgents who are linked to Al Qaeda.

The incident underlined the radicalization of the uprising, now in its third year. Western nations have largely refrained from arming the opposition, despite repeated calls from rebel groups and their Arab backers in the Persian Gulf, for fear of propping up a jihadist insurgency. Qatar and Saudi Arabia are believed to have sent weapons, seeing the civil war in Syria as part of a regional struggle for supremacy with their nemesis Iran, an ally of Assad’s.

While mainly Islamist rebels control swaths of the desert east of the country as well as towns along the northern border with Turkey, the opposition failed to stave off a government offensive in the southwest last month when loyalist forces, including fighters from Lebanon’s Hezbollah, retook control of the only highway that connects the capital Damascus with the city of Homs, long a hotbed of the insurgency.

The regime also still controls the northwestern heartland of Assad’s Alawite tribe which is the main recruiting ground for its most loyal soldiers.

Correction: An earlier version of this story stated that General Idris had fled to Qatar. It seems he already was in Qatar at the time of the described events and then returned to Turkey rather than Syria.