A female homicide bomber allegedly planning to blow herself up among Shiite pilgrims was arrested Wednesday in northern Iraq, as millions joined processions across the country to honor the martyrdom of one of their most revered saints, Iraqi police said.

Police arrested the alleged homicide bomber as she neared a procession in Balad Ruz, 45 miles northeast of Baghdad, an Iraqi police officer said.

Thousands of Iraqi security forces have been deployed to protect an estimated 2 million Shiite pilgrims joining a procession in the southern holy city of Karbala, which drew pilgrims from Iraq, Iran and other countries, said Aqil al-Khazali, Karbala's provincial governor.

The arrest of the woman, who was pointed out to police by other pilgrims, comes after a homicide bombing by a man dressed as a woman earlier this week near a Shiite shrine in Baghdad that killed 38 and wounded more than 70. The bombing led Baghdad authorities to ban women from nearing the shrine.

The police officer spoke on condition of anonymity because he was not authorized to release information to the news media.

Throughout Iraq, the government has deployed more than 30,000 policemen and soldiers in Baghdad, Karbala and on roads linking the two cities to safeguard the ceremonies. Attacks by Al Qaeda in Iraq, Sunni insurgents and even a Shiite cult have killed hundreds of people in recent years.

Ashoura observances mark the seventh century death of Imam Hussein, grandson of the Prophet Muhammad, in a battle near Karbala, 50 miles south of Baghdad, that was a key event in Islam's split into the majority Sunni and minority Shiite branches.

It is essentially a mournful occasion, but Iraq's majority Shiites have used it to showcase their dominance after decades of oppression under Saddam Hussein's Sunni-led regime, turning out in large numbers to mark the occasion despite the threat of insurgent attacks.

In Karbala, men wearing black or white robes moved rhythmically and chanted as they moved toward the golden domed mosques of Imam Hussein and his half brother Imam Abbas.

They pounded their chests, slashed their heads and beat their bloodied foreheads with the flat sides of swords and knives.

"We have come here today to express our love and dedication to Imam Hussein and to show that we are not afraid to come to Karbala despite danger," said Diyaa Fiyadh, 35, a teacher from Diwaniyah, 80 miles south of Baghdad. His head bled from the ritual beating.

Rahim Muhsin, 42, a trader from Baghdad said he was not deterred by the violence from attending the Karbala procession.

"It is a great day to reminds us of the sacrifices of our saints for the sake of justice and righteousness," he said.