Bremer left Iraq in June 2004, transferring power to the Iraqi Interim Government, which was led by Ayad Allawi. In January 2005, the Iraqi people voted on representatives for the Iraqi National Assembly, and the Shia United Iraqi Alliance formed a governing coalition led by Ibrahim al-Jaafari. In October 2005, the Iraqis ratified a new constitution that created a decentralized governmental structure dividing Iraq into communities of Sunni Arabs, Shia Arabs, and Kurds. After a December 2005 election, Jafari was succeeded as prime minister by another Shia, Nouri al-Maliki. The elections failed to quell the insurgency, and hundreds of U.S. soldiers stationed in Iraq died during 2005 and 2006. Sectarian violence between Sunnis and Shias also intensified following the 2006 al-Askari mosque bombing. In a December 2006 report, the bipartisan Iraq Study Group described the situation in Iraq as "grave and deteriorating," and the report called for the U.S. to gradually withdraw soldiers from Iraq.