Twenty-four people were killed on Monday in twin suicide bombings in Syria’s northwestern city of Idlib. The first blast was caused by a bomb planted under a car in the main city of the Idlib region, the Syrian Observatory for Human Rights said. Four children were among the casualties. A motorcycle bomb detonated after ambulances arrived at the scene of the first explosion, the Britain-based monitoring group said. Many civil defense members were among the victims. There was no immediate claim of responsibility for the attack, which the Observatory said also wounded at least 51, updating an earlier casualty toll. Idlib, the last major part of Syria still outside the control of Bashar al-Assads regime, is held by an alliance led by Syrias former Al-Qaeda affiliate, Hayat Tahrir al-Sham. HTS took administrative control of the whole of the region last month, after overpowering smaller Turkey-backed factions. The ISIS group also has sleeper cells in the area. A local office of the "Salvation Government", an administrative body created by HTS, is located on the street targeted by Mondays attack. Four HTS fighters were killed in the blast, the Observatory said, while the other 20 victims were civilians. Alliance commanders say they hundreds of people have been rounded up for suspected links to Assads intelligence services or ISIS sleeper cells who they blame for some of the bombings. They say the wave of blasts in the densely populated region, a haven for tens of thousands of civilians opposed to Assads rule, aims to destabilize the last opposition bastion remaining after almost eight years of war. Idlib has been protected from a massive regime offensive since September by a buffer zone deal agreed by regime ally Russia and opposition backer Turkey. But it has been hit by sporadic regime shelling. Eight years into the conflict that has killed more than 360,000 people, the regime controls nearly two-thirds of the country.