Police in Iraq say insurgents have killed six members of a Sunni militia allied with U.S. forces against al-Qaida. The Sahwa (Awakening) fighters were killed in a village in Diyala province on Thursday. The incident comes a day after a string of apparently coordinated attacks killed at least 55 people across Iraq.A recent surge of attacks has raised concerns about the ability of Iraqi forces to fight insurgents as U.S. troops withdraw from the country. The United States officially ends its combat mission in Iraq on August 31.