HILLA, Iraq (Reuters) - A suicide bomber detonated a vest packed with metal ball bearings in a refreshment tent full of Iraqi pilgrims heading to a Shi’ite festival on Sunday, killing 40 people and wounding 60, police said.

Women and children were among the victims in the bombing in the town of Iskandariya, 40 km (25 miles) south of Baghdad.

The attack was one of the deadliest in Iraq this year and happened despite a major tightening of security for the annual Arbain festival in the southern holy city of Kerbala. It is one of Shi’ite Islam’s holiest events.

Most of the casualties were hit by the ball bearings, said a doctor at a hospital in the city of Hilla, where many of the wounded were taken. A wounded woman there said the attack happened in a tent where pilgrims were offered refreshments.

“When we reached the area people invited us into a tent to take some rest and have some food. When we entered, there was a huge ball of fire and we saw people lying on the ground,” said Um A’amr, who was being treated for multiple wounds.

Police and the U.S. military said the bomber struck hours after militants killed three pilgrims and wounded 36 others in an attack in southern Baghdad.

Captain Muthanna al-Mamouri, spokesman for police in Hilla, 100 km (60 miles) south of the capital, said 40 people were killed and 60 wounded in the Iskandariya attack.

Colonel Tom James, a U.S. brigade commander in the area, said Iraqi forces would strengthen security at rest areas for pilgrims, but added it was “very difficult” to protect everyone. He said about 40 people had been killed in Iskandariya.

“This is a despicable terrorist attack on these innocent people,” James told Reuters, adding that ball bearings had been found at the scene of the attack.

The U.S. military said in a statement the attack took place on a two-lane highway near a residential area through which more than 40,000 pilgrims had passed earlier in the day.

Millions of Shi’ite pilgrims are expected in Kerbala for the Arbain festival this week, which commemorates the end of the 40 -day mourning period following Ashura, a religious ritual that marks the death of Prophet Mohammad’s grandson in 680.

Tens of thousands of Iraqi soldiers and police have been deployed for Arbain after suspected Sunni Arab insurgents killed 149 pilgrims on their way to Kerbala for the event last year, one of the worst spasms of violence since the U.S.-led invasion of Iraq in 2003.

The pilgrims are particularly vulnerable because many prefer to walk to Kerbala, 110 km (70 miles) south of Baghdad. They believe the effort will bring them greater spiritual reward.

A policeman mans a weapon on mounted on an armored vehicle, as pilgrims arrive at Kerbala, to attend the religious ceremony of Arbain that falls 40 days after the Shi'ite holy day of Ashura February 23, 2008. REUTERS/Mushtaq Muhammed

VEHICLE BAN

In the Baghdad attack, the pilgrims were hit by a roadside bomb and then fired on by gunmen on a road used by pilgrims walking to Kerbala, police said.

The U.S. military gave a different account, saying gunmen had lobbed hand grenades at the pilgrims in Baghdad, killing one and wounding 17.

It said U.S. and Iraqi forces would increase patrols and checkpoints, restricting vehicle access through key routes to Kerbala from southern Baghdad.

Kerbala’s police chief, Major-General Raad Shakir, told Reuters last week that 40,000 police and soldiers had been deployed and Iraqi tanks were being used to protect the city for the first time.

All public transport, including bicycles, has been banned within a 25 km (15.5 mile) radius of the city and 600 female security staff have been assigned to search women, police said.

Militants have used horses and carts, bicycles and motorcycles in bomb attacks in the past. There has also been a spate of suicide bombings carried out by women in recent months.

In previous years, militants have killed scores of pilgrims in suicide bombings and other attacks. Sunni Islamist al Qaeda views Shi’ites, a majority in Iraq but a minority in the Muslim world, as heretics.