A suicide bomber Sunday killed at least 40 Iraqi Shiite pilgrims and wounded 60 more as they were headed south to mark a Shiite religious holiday. Earlier in the day at least three pilgrims were killed in Baghdad despite officials saying security has improved. Daniel Schearf reports from the northern Iraqi city of Irbil.

Police say the bomber detonated in a tent full of Shiite pilgrims in the town of Iskandariyah Sunday as they were stopping for refreshments. Women and children were among the casualties.

The military says the attack took place on a two-lane highway south of Baghdad leading to the southern city of Karbala.

Earlier in the day at least three other Shiite pilgrims were killed and more than 30 wounded in separate Baghdad attacks as they prepared to leave for Karbala. Police said pilgrims were hit with a roadside bomb and fired on by gunmen.

This eyewitness described what happened.

He says as they were going to the holy shrine of Imam Hussein for the pilgrimage, gunmen opened fire on them in Dora, a Baghdad neighborhood. He asks why they would do that to innocent and peaceful people.

Tens of thousands of Shiite pilgrims are making their way to Karbala to commemorate Arbaeen. The Shiite ceremony marks the end of a 40-day mourning period over the death 13 centuries ago of the Prophet Mohammed's grandson, Imam Hussein.

Sunni militants consider Shiites heretics and often target Shiite pilgrims traveling for religious observances. Scores were killed during last year's pilgrimage.

The attacks occurred despite stepped-up security measures around Baghdad and Karbala aimed at preventing attacks on pilgrims.

The police chief of Karbala had deployed 40,000 officers to secure the city.

Iraq's Interior Minister Jawad Polani on Saturday evening toured security checkpoints around the south of Baghdad. He declared roads connecting to the city from the south safe for travel.

Millions of Shiites are expected in Karbala for the commemoration Wednesday.