By Wisam Mohammed and Sami al-Jumaili

KERBALA, Iraq (Reuters) - A female suicide bomber blew herself up in a crowd of Shi'ite pilgrims on Friday, killing 32 people and wounding 84 others south of Baghdad during one of the holiest events of the Shi'ite calendar, police said.

The attack on the pilgrimage route in Iskandariya, 40 km (25 miles) south of the capital, came a day after a bomb killed eight in the Shi'ite holy city of Kerbala, to which hundreds of thousands if not millions were headed to mark Arbain.

Arbain is one of the most important Shi'ite Muslim rites, and marks the end of a mourning period after the anniversary of the death in battle in the seventh century of the Prophet Mohammad's grandson Imam Hussein.

Some pilgrims, hardened to attacks by suspected Sunni Islamist insurgents in the years since the 2003 U.S.-led invasion, said the bombs would not deter them.

"We came here for the pilgrimage. Nothing will stop us. We aren't afraid. We've been through worse events in the past," said 63-year-old Sadia Ali, who had traveled to Kerbala from Baghdad's Sadr City slum.

The attacks occurred despite heavy security on the pilgrimage route. The ranks of troops and police patrolling Kerbala were boosted by 5,000 to 30,000, a city official said.

The Arbain rite, which culminates early on Monday, is difficult to secure. Many pilgrims walk all the way to Kerbala, and are easy targets as they cover hundreds of miles clutching religious banners.

Shi'ite religious rites have drawn huge crowds in Iraq since the invasion that toppled the Sunni-led government of Saddam Hussein, who curtailed large Shi'ite gatherings.

The events have been regular targets of Sunni insurgents such as al Qaeda during the sectarian bloodshed that followed Saddam's fall. Al Qaeda views Shi'ites as heretics. A suicide attack during Arbain last year killed 63 people.

"These cowardly actions will not undermine the determination and patience of the pilgrims. We call upon our people and especially the security forces to take more precautions and be alert," said a statement on the website of Ayatollah Sadiq al-Husseini al-Shirazi, a member of Iraq's top Shi'ite clergy.

HIGH ALERT

Many women and children were among the dead and wounded in Friday's attack, police said. Emergency services were on high alert, and people were asked to give blood as a precaution.

"I have been sleeping in the ambulance," said emergency worker Ahmed Kadhom.

Kadhom said that after Thursday's attack, he saw a grief-stricken man carrying his dead young son.

"He was shouting and crying. I will never forget this scene," he said.