In the past week, Islamic State Sunni militants who overran the city of Mosul last month have rounded up between 25 and 60 senior ex-military officers and members of former dictator Saddam Hussein's banned Baath party, residents and relatives say. The northern city of around 2 million people is by far the largest to fall to the Islamic State group and a central part of its plans for an Islamist caliphate. When the group, then known as the Islamic State in Iraq and the Levant, seized large swathes of Iraq at lightning speed last month, it was supported by other Sunni Muslim armed groups. Tribes and former loyalists of Saddam's Baath party were eager to hit back at Iraq's Shi'ite leaders, even if they did not share ISIL's vision of a caliphate ruled on mediaeval Islamic precepts. But now, leaders of those groups are being ordered to swear allegiance to the new caliphate. "I think (the Islamic State) wants to give the message that they are the only group in the land, that people must follow them or give up their weapons," said provincial governor Atheel Nujaifi, who is in touch with residents by phone after having fled to the Kurdish-controlled city of Arbil as Mosul fell. Shi'ite parliamentarian Haidar Abadi said the Islamic State was taking pre-emptive action to head off potential challenges. "ISIL knows very well they can't stay if these groups move against them. They are not giving them the opportunity." "ISIL called on their friends who are ex-Baathists to cooperate and they did. And now ISIL is kicking them out. Some will pledge allegiance. Those they don't believe will pledge allegiance, they will execute," he said. An Iraqi national intelligence officer, confirming the arrest by militants of Saddam-era officers, said the motive was: "to panic people, or as revenge, or in the event that they would cooperate with the Iraqi government". Nujaifi, the governor, estimated that around 2,000 Mosul residents had signed up to join the Islamic State as fighters since they took the city. But he said career army officers and diehard Baathists were unlikely to be won over to ISIL. FAMILIAR TACTICS The governor and some residents told Reuters that they believe ISIL's bold declaration of a caliphate last week had caused local discontent, possibly prompting the group to act to head off the first stirrings of resistance. The move echoes Islamic State tactics in neighbouring Syria, where the group, an offshoot of al Qaeda, entrenched itself in the rebel-held east by eliminating other opponents of President Bashar al-Assad. Although ISIL, the Sunni tribes and veterans of Saddam's Baath party emerged as allies last month, they have a history of enmity. Many of those nostalgic for Saddam teamed up with Sunni tribes to fight against the Islamic State's predecessor, Al Qaeda in Iraq, during the U.S. "surge" offensive in 2006-2007. http://english.ahram.org.eg/News/105773.aspx