BAGHDAD - Iraqi troops battled to dislodge an al Qaeda splinter group from the city of Tikrit on Monday after its leader was declared caliph of a new Islamic state in lands seized this month across a swathe of Iraq and Syria. Alarming regional and world powers, the Islamic State in Iraq and al-Sham (ISIS) claimed universal authority when it dropped the local element in its name and said its leader Abu Bakr al-Baghdadi, as leader of the Islamic State, was now caliph of the Muslim world - a medieval title last widely recognized in the Ottoman sultan deposed 90 years ago after World War One.

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The move, which follows a three-week drive for territory by ISIS militants and allies among Iraqi's Sunni Muslim minority, aims to erase international borders drawn by colonial powers and defy Baghdad's U.S.- and Iranian-backed, Shiite-led government. It also poses a direct challenge to the global leadership of al Qaeda, which has disowned it, and to conservative Gulf Arab Sunni rulers who already view the group as a security threat. Tikrit was the home city of Saddam Hussein, whose overthrow by U.S. forces in 2003 ended a long history of domination by Sunnis over what is today a Shiite majority in Iraq.

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