Iraq ? Underlining the continued threat of sectarian violence in Iraq, a suicide bomber blew himself up in a crowd of Shiite pilgrims south of Baghdad on Sunday, killing at least 40 as they headed for the city of Karbala for the holiest Shiite festival of the year.

It is traditional for Iraqi Shiites to walk to the holy city of Karbala for the Arbaeen festival, commemorating the 40th day after the death in 680 of the Prophet Muhammad’s grandson, Hussein, the most revered figure in Shiite Islam – though under Saddam Hussein the observance was routinely suppressed.

Since the U.S. invasion in 2003, it has also become a tradition for al-Qaida in Iraq to target the pilgrims along the way, part of the pattern of sectarian violence that has engulfed Iraq. Police blamed al-Qaida for the latest attack.