BEIRUT/DAMASCUS — Rebels seized an air defense base near Syria's strategic southern international highway on Saturday, activists said, a gain that could bolster opposition fighters trying to secure supply routes to the capital Damascus. Syria's southern provinces bordering Jordan and Israel have become an increasingly significant battleground as the embattled capital comes into play, with President Bashar Assad's forces and his loyalist militias hitting back hard to prevent rebel advances. The Britain-based Syrian Observatory for Human Rights, which has a network of sources among activists across Syria, said among those killed was the base commander after a two-week battle for the site in Deraa, a province bordering Jordan where initially peaceful protests against Assad set off Syria's two-year uprising. “Fighters from the Nusra Front, Yarmouk Martyrs Brigade, and other battalions seized control of the 38th division air defense base, near the town of Saida on the Damascus-Amman highway, after 16 days of fierce clashes,” the Observatory said. A video uploaded by the Observatory, showed what it said was the body of Gen. Mahmoud Darwish, commander at the base, lying in a pool of blood in a bathroom. It was not immediately possible to verify the pictures or activist report. Clashes have also raged near the border with Israel, which is growing concerned that Islamist rebels may be emboldened to end the quiet on the Golan front maintained by Assad and his father before him during their four decade rule of Syria. Rebels last Wednesday overran at least three towns near the Israeli-Syrian disengagement line but appeared to lose ground after militias loyal to Assad pushed them back in a fierce battle. Rami Abdelrahman, head of the Observatory, said the pro-government militias involved were made up of fighters from Syria's Druze minority, a sect which for some time had stayed on the sidelines of the conflict but now increasingly appears to be swinging its weight behind Assad. Their involvement could increase sectarian bloodshed in Syria, already wracked by tensions between the Sunni Muslim majority that has led the uprising and the Alawite minority to which Assad belongs. Tit-for-tat kidnappings and killings between the sects have become common as the uprising spiraled into a bloody civil war that has killed more than 70,000 people. Meanwhile, supporters of Assad gathered in downtown Damascus amid tight security on Saturday for the funeral of one of Syria's best-known clerics who was assassinated in a brazen mosque bombing earlier this week. Security forces sealed off all roads leading to the eighth century Omayyad Mosque where the funeral for Sheikh Mohammad Said Ramadan Al-Buti, an 84-year-old pro-government cleric, was held. Al-Buti, his grandson and 48 others were killed Thursday when a suicide bomber detonated his explosives inside a mosque where Al-Buti was giving a religious lesson. 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. — Reuters