BEIRUT (AP) -- Syrian regime forces routed rebels in fighting on the edge of the Israeli-occupied Golan Heights last week, leaving at least 35 dead, activists said Saturday, as the country's civil war reached the doorstep of the strategic plateau.
The rebel effort to overrun the Quneitra region along the cease-fire line separating Syria and Israel has heightened worries that Islamic extremists among those fighting President Bashar Assad could take over the front line with Israeli troops and gain a potential staging ground for attacks on the Jewish state.
The frontier has largely been calm in the nearly four decades since the two countries fought a war over the Golan Heights that ended with a U.N.-monitored cease-fire. But Israeli military officials have expressed concern that a rebel takeover could upset the calm maintained by Assad and his predecessor and father the late Hafez Assad.
Those fears have been compounded by increasing influence wielded by extremist groups over the divided rebels and the increasing international isolation of the regime.
"We are seeing terror organizations gaining footholds increasingly in the territory," said Lt. Gen. Benny Gantz, Israel's military chief at a conference in Israel last week. "For now, they are fighting Assad. Guess what? We're next in line."
One of the worst-case scenarios as Syria enters its third year of conflict is that neighboring countries such as Israel or Lebanon could be drawn in.
Israel says it is trying to stay out of Syria's civil war, but it retaliated for sporadic Syrian fire that spilled into Israeli communities on the Golan Heights on several occasions over the past few months.
When Israel bombed targets inside Syria said to include a weapons convoy headed for Hezbollah in Lebanon in January, Syrian opposition fighters derided Assad for not retaliating.
The Syrian rebels are made up of dozens of groups including the powerful, al-Qaida-linked Jabhat al-Nusra, which has been labeled a terrorist organization by the Obama administration. One of the groups involved in the Golan fighting, the Yarmouk Martyrs Brigade, is an Islamic militant group.
The rebels have largely been beaten back since they seized control of at least one Druze village and parts of several others in Quneitra province near the 1974 disengagement line.
The Britain-based Syrian Observatory for Human Rights said it had documented the deaths of 35 opposition fighters and contact had been lost with more than 20 others believed to have died in the fighting Wednesday and Thursday.
At least six pro-Assad fighters were also killed and dozens of others were wounded, according to the activist group.
For now, opposition fighters in Syria appear to be focused on toppling Assad, and there is little to suggest that they may be planning to turn their guns on Israel.
Rami Abdul-Rahman, director of the Observatory, said fighters were rallied around the same goal of ousting Assad. "But when there's chaos, who knows what might happen," he said.
Anthony Skinner, Middle East-North Africa chief at the British risk analysis firm Maplecroft, said the number of armed groups fighting in Syria makes it difficult to predict whether militant Islamists would contemplate an attack on Israel if the opportunity arose.
"Pragmatists would not want to provoke a riposte from Israel that could potentially play into Bashar Assad's hands," he said.
Skinner and other analysts said the fall of Quneitra on its own would be unlikely to trigger Israeli intervention, which would increase the risk of a war with the Syrian-backed Lebanese Hezbollah militant group.
"The worst thing Israel could do is get involved. Right now there is no immediate danger for Israel and it shouldn't get involved," said Eyal Zisser, professor of Middle Eastern studies at Tel Aviv University.
The Golan front has been mostly quiet since 1974, a year after Syria and Israel fought a war during which Damascus tried to retake the plateau, and briefly captured Quneitra, before the two sides agreed to disengage from the area.
The United Nations Disengagement Observer Force, known as UNDOF, was established to monitor the cease-fire in May 1974 by a U.N. Security Council resolution.
An Israeli military official this week said the entire border area has become a "playground" for skirmishes between rebels and the Syrian army.
Last month, members of the Yarmouk Martyrs Brigade held 21 Filipino peacekeepers hostage for four days, raising concerns about the future of U.N. operations in the area.
Syrian rebels in recent weeks have been making inroads in towns and villages in the frontier area stretching from the border with Jordan in the south to suburbs southwest of the capital, Damascus.