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 Thursday, a day after a string of apparently coordinated attacks killed at least 55 people across Iraq.

A series of car bombings and other attacks Wednesday mostly targeted Iraqi security forces in one of the worst days of violence in months.

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.

Some 50,000 troops are to remain in the country to train and advise Iraqi forces until the end of 2011, when all U.S. forces are to leave.

Some information for this report was provided by AP and AFP.

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