Iraqi officials say bombs have exploded among Shi'ite pilgrims marking the holy day of Ashura, killing at least six people and wounding more than 30 others.

Sunday's deadliest blast was in the northern Iraqi town of Tuz Khormato, about 180 kilometers north of Baghdad. A roadside bomb exploded during a pilgrims' procession, killing five and wounding 28.

In the capital, a bomb exploded in Baghdad's Mansour district, striking a mini-bus carrying Shi'ite pilgrims.  One pilgrim was killed and several others were wounded.

Millions of Shi'ites joined processions across Iraq Sunday, the high point of the solemn 10-day religious observance.

Authorities say an estimated three million pilgrims were taking part in the main procession in the Shi'ite holy city of Karbala, home to the shrine of Imam Hussein.

No attacks were reported in and around Karbala, where Iraqi authorities deployed an extra 25,000 security personnel to prevent violence.

In the days leading up to Sunday, attacks on Shi'ite pilgrims across Iraq had killed at least 20 people and wounded more than 100 others.  Sunni militants have targeted Shi'ite observances in Iraq in the past.

Former Iraqi leader Saddam Hussein, a Sunni, strictly limited Ashura rituals during his rule.  Since his overthrow by U.S.-led forces in 2003, Ashura has become a show of strength for Iraq's majority Shi'ites.

Men beat their heads and chests in ritual acts of mourning for the seventh-century killing of the imam, a grandson of the Prophet Muhammad. 

Some information for this report was provided by AP, AFP and Reuters.