A state funeral service for six Italian soldiers killed in a suicide attack in Afghanistan is being held on what has been declared a national day of mourning.Thousands of people lined the route to the church of Saint Paolo in Rome. The suicide bombing caused the single biggest loss of life suffered by Italian forces in Afghanistan. The troops were killed when their convoy came under attack in the Afghan capital Kabul. They were part of the Italian contingent of the NATO-led International Assistance Force or ISAF. Italian Prime Minister Silvio Berlusconi was among the mourners. The attack has sparked renewed debate in Italy over the withdrawal of its 2,800 troops from Afghanistan. The latest deaths bring to 21 the number of Italian soldiers killed since the start of the Afghan conflict in 2001. The bombing also claimed the lives of 10 Afghan civilians and injured dozens more. The Taliban claimed responsibility for the attack.