The attack took place on the highway between Tuz Khurmatu and Tikrit.

The anti-Al-Qaeda fighters or Sahwa as they are called are a collection of tribal militias that turned against Al-Qaeda and sided with the US military from late 2006 onwards, helping turn the tide against Iraq's bloody insurgency.

The militiamen are regarded as traitors by militants and are frequently targeted in attacks.

With the latest violence, over 165 people have been killed in attacks in the first eight days of July -- far more than in the whole month of December, according to figures based on security and medical sources.

Iraq has seen a surge in violence since the beginning of the year, coinciding with ongoing protests in the Arab community that analysts and diplomats say have boosted recruitment to militant groups and given them room to manoeuvre.