BAQUBA: A car bomb in a restive town north of Baghdad on Friday killed six Iranian pilgrims, officials said, the latest in a spike in violence that has sparked fears of all - out sectarian war. A further 23 worshippers were wounded in the attack, which struck their bus as it was passing through the town of Muqdadiyah en route from the Iranian border to the holy Shia city of Najaf. Najaf, which lies south of Baghdad, is home to a shrine to a revered figure in Shia Islam. Shia Muslims visiting holy shrines and religious sites form the backbone of Iraq's tourism industry, with the vast majority of such visitors coming from Iran. When completing a tour of Iraq's key Shia religious sites, pilgrims typically visit Najaf, nearby Karbala, Baghdad, and Samarra, the latter of which lies north of the capital. No group immediately claimed responsibility for Friday's bombing, however.