BAQUBA - A car bomb in a restive town north of Iraq’s capital killed 10 Iranian pilgrims Friday, officials said, the latest in a spike in violence that has sparked fears of all-out sectarian war.

Another 30 pilgrims 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 Shiite holy city of Najaf.

Shias visiting holy shrines and religious sites form the backbone of Iraq’s tourism industry, with the vast majority of pilgrims 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. But militants, including those linked to Al-Qaeda, often target them for attacks. No group immediately claimed responsibility for Friday’s bombing, however. Attacks in Iraq have risen sharply, with May the country’s deadliest month since 2008.