Concerned about the possible drift of al-Qaeda affiliates to areas adjacent to the Golan Heights border, Israel finds itself obliged to increase its assistance to local rebel militias in southern Syria.

As the fighting in Syria rages, Israel has been moving cautiously and often reluctantly toward assuming a modest role in the civil war, restricted to areas along the Golan Heights frontier line. What began as a purely humanitarian step -- extending emergency medical aid to injured and sick Syrians from neighboring villages -- has by now reportedly expanded into a well-developed mechanism for providing a whole range of items, from medications to food, fuel, clothes, heaters, and more. One should assume that the same understandings which allowed over 600 wounded Syrians to be evacuated for treatment in Israeli hospitals -- including a special military field hospital on the Golan -- are facilitating other forms of assistance as well. A significant operation of this type indicates that a system of communications and frequent contacts have been established with the local rebel militias, since the evacuation of the injured and their return to Syria seem to function flawlessly.

These developments bring to mind the establishment of "The Good Fence" along the Israel-Lebanon border when civil war erupted there in the mid-1970s. Yet unlike in Lebanon, the Israeli forces involved in the current Golan-based assistance effort have been very careful not to operate inside Syrian territory or assume responsibility for the villages in question, most of which are populated by a mixture of Sunnis, Druze, and Circassians, along with various armed factions.

Israel initially opted to remove itself from the bloody quagmire in Syria. It even accepted without protest its exclusion from the latest Geneva II peace conference, despite Israel's major stake in how the conflict is settled and its longstanding bilateral accord with Syria -- the 1974 Separation of Forces Agreement, which is still in effect. Yet Israeli concerns about the war's consequences have been aggravated by the emergence of al-Qaeda affiliates and other radical Islamist militias, which have gained preeminence among rebel units in many parts of central and northern Syria. Israel apparently may feel obliged to take unpublicized measures aimed at preventing or at least slowing the movement of such fighters to territory south of Damascus, particularly those representing the al-Qaeda affiliates Jabhat al-Nusra and the Islamic State of Iraq and al-Sham (ISIS).

The area in question stretches from the Golan frontier up to Mount Druze in the east, and between the southern suburbs of Damascus and the city of Deraa, where the Syrian uprising was first ignited in 2011. The local militias formed in this region's villages are recognized as a potentially effective barrier to a takeover by al-Qaeda disciples. Although Jabhat al-Nusra has established a presence in the vicinity of Deraa and close to the meeting point of the Rukkad and Yarmouk Rivers, the overall situation in the south does not follow the pattern witnessed in other parts of Syria, where radicals have asserted themselves at the forefront of the rebellion.

For example, military commanders have the last word in other parts of the country, but southern militias are often directed by civilian elders. Many of them have come to view Israel as a temporary ally under the present circumstances. Emboldened by their belief that the Israel Defense Forces will indirectly protect their back, these militias have battled troops from the Assad regime's 90th and 61st Brigades, which are based in the area. When regime artillery units fire on rebel formations along the Golan frontier and an occasional stray shell lands on the Israeli side of the border fence, the IDF is indeed quick to retaliate with a single Tammuz missile directed at the position from where the shells were fired. Otherwise, however, the IDF refrains from any intervention, even when clashes occur very close to Israeli positions, sometimes with regime tanks driving within meters of the border.

President Bashar al-Assad's main interest in the south is to ensure the safety of the main highway between Damascus and Deraa and maintain a hold over parts of the latter city. He has also ordered his generals to retain Quneitra, the capital of the district bordering Israel, as well as the stretch of Druze villages to the north along the eastern slopes of Mount Hermon. So far, the regime has managed to achieve these goals and does not seem worried about losing its grip on the rest of the region, which has little strategic significance for the outcome of the current struggle.

The regime is also keen on keeping the southern Druze community out of the fight. Based mainly on Mount Druze east of Deraa, this community could play a major role in shaping realities on the ground in the south. For now, it prefers to sit on the fence until Assad's prospects of survival are clarified. Traditionally, though, Syrian Druze have special ties to the Hashemite court in Jordan and were once considered by Israeli strategist Gen. Yigal Allon as natural future allies of the Jewish state.

For their part, Israel and Jordan share similar interests in southern Syria. King Abdullah II is no less worried about the possible appearance of numerous al-Qaeda militants along his border. Accordingly, Amman is cultivating an array of local militias close to the long frontier with Syria, taking advantage of the fact that many inhabitants of southern Syria and northern Jordan belong to the same tribes. There are also many reports -- repeatedly dismissed by Jordanian authorities -- of a clandestine "operations room" in Amman where Jordanian military and intelligence officers coordinate military assistance to local rebel groups alongside Saudi and Western advisors. If such reports are correct, the Israeli part of the effort should be viewed as complementing but not necessarily coordinated with the Jordanian endeavor.

In all likelihood, the inability of al-Qaeda affiliates to seize the leading role in the south is due not only to alleged Israeli or Jordanian involvement, but also to the jihadists' preoccupation with the war in the north, where ISIS has been battling with the Islamic Front and rival group Jabhat al-Nusra (backed by al-Qaeda leader Ayman al-Zawahiri) in recent weeks in addition to fighting the regime. Yet ISIS and Jabhat al-Nusra have dramatically increased their strength -- according to Israeli intelligence estimates, they now total 40,000 men. If they launched a concerted effort to extend their foothold to the south, they would pose a major test to local militias that have yet to be seriously challenged. In that scenario, Israel and Jordan would have to decide whether to sit idly while al-Qaeda becomes entrenched along their borders.

In light of these concerns, preventing the southward expansion of extremist Islamist groups is becoming a larger priority in tackling the overall Syrian problem. If al-Qaeda affiliates take charge of the regions bordering Israel and Jordan, new terrorist threats would arise, potentially exporting Syria's bloodshed to its neighbors. Such a development would give al-Qaeda freedom of action over a vast area stretching from west of Baghdad to southern Syria. Put another way, the organization would have achieved its long-sought objective: a front with Israel.

Ehud Yaari is a Lafer International Fellow with The Washington Institute and a Middle East commentator for Israel's Channel Two television.