Masked gunmen assassinated the deputy director general of the state-run North Gas Company (NGC) Tuesday morning in Kirkuk.Iraq’s northern oil sector has been buffeted by violence in recent years, due to attacks by militants from the self-proclaimed Islamic State (IS) group, friction between rival political factions, and mafia-style violence.Tuesday’s incident echoes a series of assassinations in 2015 that targeted senior Kirkuk-based oil officials.Mohammed Younis Salih Kali was being…