Isis has launched a surprise attack on the Kurdish-controlled city of Kirkuk in Iraq, its first major incursion into an Iraqi city outside its control in months. Suicide bombers and snipers attacked the oil-rich city early on Friday morning, just days after Kurdish and Iraqi ground forces began this week’s much-heralded offensive to recapture the northern Iraqi city of Mosul. The move on Kirkuk underlines the continued threat posed by Isis as Iraq struggles to oust the jihadi group from the last 10 per cent of territory it controls in the country. The timing may also be aimed at shaking the unprecedented united front presented by the central government and Iraq’s semi autonomous Kurdistan Regional Government (KRG), which for years have been at odds over oil revenues and control of territory. They have depicted Mosul as a battle where the Iraqi military and Kurdish peshmerga forces are fighting side by side. “There has never been a militant attack like this on Kirkuk. The goal is to shake our security,” said the city’s deputy governor, Rakan Said al-Juboori. “There is still fighting in some neighbourhoods. We believe the attack was launched by sleeper cells.”