ON SYRIA’S 360km-long border with Jordan, rebel fighters are not waiting for anyone else to come and clobber Bashar Assad’s regime; they are resolved to do it themselves. They claim to control 100km (60 miles) of the frontier’s more fertile western segment, with forces reaching up to 40km north towards Damascus. On September 11th, Mr Assad’s birthday, reports suggested a significant new advance. At the start of what may prove the biggest battle yet in this region, rebel sources claimed that a force of some 8,000 fighters had captured the northern approaches to the city of Deraa. If so, they have encircled a large government garrison that has been pounding rebel-held villages with artillery.

If Deraa were to fall, it would be a signal victory. It is a more important strategic prize than the town of Qusayr on the Lebanese border, the fall of which to Mr Assad’s army in May was heralded as turning the tide in his favour. Along with a heavily fortified border-post farther south, it represents the government’s last stronghold in Syria’s south-west corner. This offensive is the fruit of months of preparation, and the result of quietly intensified efforts by the rebels’ main supporters, Saudi Arabia, the United Arab Emirates and America’s CIA, which is providing some arms. Jordan, now home to some half a million Syrian refugees, has provided a discreet conduit for the flow of arms, equipment and personnel, taking care that it does not go to extreme Islamist groups, as aid through Turkey and Iraq often does.