Syrian war planes on Friday bombed Islamic State of Iraq and Syria fighters trying to advance into the northeastern city of Hassakeh in an offensive that is adding to the pressure on President Bashar al-Assad following recent defeats elsewhere. The Syrian Observatory for Human Rights, which monitors the war, also reported fierce battles between ISIS militants and the army backed by allied militia on the city's southern outskirts. The Syrian regime has already lost Raqqa to ISIS militants and Idlib to other rebel factions. According to Rami Abdel-Rahman, director of the Syrian Observatory, ISIS militants are "500 meters away from the entrance of Hassakeh, after fierce clashes against regime forcers south of the city." Control of the city is divided between regime and Kurdish forces who have confronted ISIS in other areas of the province of Hassakeh. A dozen explosive-packed trucks have been blown up by ISIS bombers at Syrian army checkpoints around Hassakeh over the past five days, the governor said on Thursday according to Reuters. "More than thirteen explosive-laden vehicles have attacked army checkpoints and sowed terror and fear among citizens," City Governor Mohammad Zaal al Ali told state television by telephone from inside the city. Despite the attacks, the militants have been repelled and the army was manning new checkpoints across Hassakeh. ISIS has been stepping up lightning attacks on the southern edge of the ethnically mixed city, which is divided into zones run separately by the government of President Bashar al-Assad and a Kurdish administration. The Kurds have a well-organized militia which receives air support from a U.S.-led alliance and has been pushing back the militants further north west along the Turkish border.