A car bomb was detonated on Saturday in the rebel-held city of Azaz in northern Syria, killing at least 43, a monitor group said. The car was detonated near the a rebel-run courthouse in Azaz in the northern countryside of Aleppo province in northern Syria, near Turkey, according to the Syrian Observatory for Human Rights. Meanwhile, other activists placed the death toll at 50. Azaz has changed hands among rebel groups including the Islamic State several times since falling out of the government control in 2012. The recent attack is believed to have been carried out by the IS, which withdrew from the city in 2014, as since 2015 the city control has become shared between the al-Qaida-linked Nusra Front and the Turkey-backed Free Syrian Army. The city is highly valued as a logistical supply route close to the Turkish-Syrian border. The latest explosion comes as the country is observing a nationwide ceasefire brokered by Russia and Turkey since last week.