ABU Musab al-Zarqawi’s death raised hopes that Iraq’s slide toward civil war or sectarian disintegration could be arrested. But evidence in the early days of post-Zarqawi Iraq indicates Shi’ite-Sunni violence may have moved beyond the control of the insurgency’s leadership.Zarqawi, played a key role in stoking Shi’ite-Sunni tensions, launching hundreds of attacks against Shi’ites and issuing vitriolic tirades to deepen a schism that dates back 1,400 years.In a web statement posted today the al-Qaeda in Iraq named Abu Hamza al-Muhajer as the group’s new leader to succeed Zarqawi. The name al-Muhajer, Arabic for “immigrant”, suggested he was not Iraqi.On Sunday, al-Qaeda in Iraq appeared to have answered Iraqi and US questions about the future plans and tactics of the organisation that Zarqawi founded. In an Internet statement, the group vowed ‘‘to prepare major attacks that will shake the enemy like an earthquake and rattle them out of sleep.’’General George Casey, the commander of US forces in Iraq, said he took the threat seriously but suggested a surge in al-Qaeda rhetoric showed the insurgency was ‘‘hurting.’’“Now, that said.it still has the capability to generate terrorist attacks across Iraq,’’ he said on CBS’ ‘‘Face the Nation.’’Iraqi and American officials said on Sunday they planned a new security crackdown in Baghdad in response to the threats. Iraq’s new Sunni Arab Defense Minister, Abdul-Qader Mohammed Jassim al-Mifarji, said a security plan was to be put in place around Baghdad to deal with a possible surge in terror attacks.