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.
On Saturday, they seized control of a major air defense base used by the 38th Division after a 16-day siege in the south near the Jordanian border, killing its commander, activists said. The Yarmouk Martyrs Brigade also announced in a statement on its website that the base had been seized.
They also seized several army checkpoints, clearing a 25-kilometer (15-mile) stretch along the Syrian-Jordanian border, according to the Observatory.
Islamic extremists have risen in the mostly Sunni rebel ranks, thanks in large part to their superior organization and recruiting skills. That has led to a rise in suicide attacks targeting Assad's regime, including a bombing Thursday that killed 50 people, including one of Syria's best-known pro-government Sunni clerics, inside a Damascus mosque.
Mourners lifted the coffins of Sheik Mohammad Said Ramadan al-Buti and his grandson who also was killed, draped in white cloth, on their shoulders amid shouts of "God is Great" during the funeral procession on Saturday in Damascus.
Security forces sealed off all roads leading to the landmark eighth century Omayyad Mosque for the funeral of the 84-year-old cleric, who was the mosque's imam, was held.
His assassination was a blow to Assad, who vowed Friday to avenge his death, saying he would "purge" the country of the militants behind the attack in the heart of the capital.
Mourners carried al-Buti and his grandson's coffins, draped in white cloth, on their shoulders amid shouts of "God is Great."
Church bells tolled and mosque minarets in the ancient city blared "God is Great" during the funeral procession. State TV said al-Buti was buried in a courtyard at the rear of the mosque near the tomb of Saladin, a medieval Muslim warrior.
The choice enraged many among the opposition who considered it an affront to Syria's history and cultural heritage.
In Egypt, members of Assad's own minority sect who are opposed to his regime began a two-day meeting that organizers described as the first of its kind to discuss concerns about their fate in a post-Assad Syria.
Rebels fighting to end Assad's rule are mostly from the country's majority Sunni sect. Assad is Alawite, a Shiite offshoot of Islam.
Members of the Alawite community who make up about 12 percent of Syria's population have either rallied behind Assad or stayed quietly on the sidelines of the civil war.
The meeting of about 50 Alawites reflects fear the minority would fall victim to revenge killings and assassinations should Assad's regime fall.
They plan on seeking assurances from opposition chief Mouaz al-Khatib who may attend the meeting on Sunday.
Associated Press Writer Albert Aji in Damascus, and Josef Federman and Ian Deitch in Jerusalem contributed to this report.
Copyright 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.