Iraq has issued an arrest warrant for a militant believed to be responsible for the 2003 truck-bombing of the United Nations headquarters in Baghdad, the U.S. military said in a statement. The attack killed 22 people including U.N. envoy Sergio Vieira de Mello.The statement yesterday said Iraq's Central Investigating Court had issued the warrant on December 4 for Mullah Halgurd al-Khabir. It named him as the prime suspect for the U.N. headquarters attack and said he was the senior leader in Baghdad of the Army of Ansar al-Sunna -- one of the main Sunni insurgent groups in Iraq. It also said Khabir had historical ties to Abu Musaab al-Zarqawi, al Qaeda's leader in Iraq.