Rebels fighting the regime of President Bashar al-Assad on Saturday seized a key air base in the southern Syrian province of Daraa after two weeks of fierce battles with loyalist troops, a watchdog said. Meanwhile, in Damascus's ancient Umayyad mosque, thousands of Assad supporters attended the funeral of pro-regime Sunni cleric Mohamed Saeed al-Bouti and his grandson, who died in a Thursday suicide bombing that killed some 50 people. "Opposition fighters loyal to al-Nusra Front, al-Yarmuk Brigade and other rebel groups seized air defence Base 38 near the town of Saida, on the road linking Damascus to Amman, in the province of Daraa," said the Syrian Observatory for Human Rights. The seizure came "after 16 days of fighting," said the Britain-based group. At least seven rebels were killed in their final assault on the base, said the Observatory, which also documented the deaths of at least eight regime troops including an officer. "Dozens of prisoners were freed from the base's headquarters," it said. Amateur video filmed by rebels and distributed by the Observatory showed the bloodied, mutilated corpse of a man identified as Mahmud Darwish, an officer. Activists also distributed footage showing a group of men, most of them bearded, being set free. The Syrian Revolution General Commission, a network of activists on the ground, said the rebels also captured a checkpoint in the Daraa town of Sahem al-Golan. The Observatory later reported that rebels captured a second checkpoint east of Sahem al-Golan. Amateur video showed rebels seizing at least two regime tanks and several military vehicles after they captured the checkpoint. "I swear to God, we are coming for you, O Bashar," a rebel said in a video distributed by anti-regime activists. The rebel advances came days after rebels seized a border crossing on the frontier with Jordan, said the Observatory. A security source in Damascus told AFP this week that Jordan was allowing jihadist fighters and arms bought by Saudi Arabia from Croatia to be smuggled into Syria. In Quneitra, meanwhile, at least 35 rebels were killed on Wednesday and Thursday fighting troops loyal to Assad, said the Observatory. Some 20 other fighters were also believed dead after battles in majority Druze villages in Quneitra province, which lays on the sensitive ceasefire line with Israel. In the central city of Homs, troops pressed a relentless campaign against rebel enclaves after more than nine months of a suffocating siege by the army and security forces. At Bouti's funeral in Damascus, Syria's top Sunni authority Mufti Ahmad Badreddine Hassoun called on "the Islamic and Arab world to save Syria, which is facing a global war. "If Syria falls today you will be next," he said before thousands of mourners. The ceremony was led by Toufiq Bouti, the dead sheikh's son, and representatives of key Damascus allies Iran and Hezbollah also attended. The United Nations estimates that violence across Syria has killed at least 70,000 people since the conflict erupted in March 2011. On Saturday alone, at least 64 people were killed in violence across Syria, according to the Observatory, which added that at least 24 of them were civilians.