At least 15 people were killed in a regime attack in Syria's northwestern Idlib province Monday, local sources have said.A regime warplane struck a fuel market in Idlib, killing 15 people and injuring 40 others, civil defense sources told Anadolu Agency.The attack has left several shops in flames, the sources said, while many of the injured admitted to hospitals were suffering from serious burns.Syria has been locked in a vicious civil war since early 2011 when the Assad regime cracked down on pro-democracy protests with unexpected ferocity.Since then, more than 250,000 people have been killed and more than 10 million displaced, according to the UN.Last week, the U.S. and Russia brokered a cessation-of-hostilities agreement between the Syrian regime and opposition forces. Russia has been staging airstrikes against positions held by Assad's opponents since last September.