Updated

Police questioned two brothers Wednesday for alleged involvement in a blast that killed a toddler and triggered a stampede that injured dozens of people in a holy Indian city.

The bomb hidden in a metal canister exploded Tuesday evening as thousands gathered for a daily Hindu ritual on the banks of the Ganges River in Varanasi city. It was the fourth bomb attack in Varanasi in the past five years.

India's Home Minister Palaniappan Chidambaram said Wednesday a warning of a possible attack was received three days before the bombing and security was heightened. Laxity by police may have occurred, Chidambaram said.

The bomb was stashed in a milk container on the Sheetla Ghat, one of many stone staircases leading to the Ganges — the site of daily spiritual rituals, according to police official Brij Lal. A 2-year-old sitting on her mother's lap when the bomb went off died in a hospital, Lal said.

The explosion and subsequent stampede injured 31 people, including four foreigners, Chidambaram said after visiting the site.

A banned Muslim terrorist group allegedly claimed responsibility for the blast in an e-mail sent to several media outlets soon after the explosion. Police were checking the veracity of the claim by Indian Mujaheddin.

The two detained men were arrested in Mumbai, India's financial hub, after investigators determined the e-mail claiming responsibility was sent from a laptop belonging to the two, a senior police official said on condition of anonymity, because he was not authorized to speak to the media.

Chidambaram didn't identify the foreigners injured. Local police said they included an Italian, a French national and one Japanese.

Chidambaram said the attack site was identified as a possible target as early as February this year. He said Uttar Pradesh state police were warned again Sunday on the eve of the anniversary of the 1992 demolition of the 16th century Babri mosque by Hindu hard-liners in the eastern town of Ayodhya.

State police tightened security but the attackers still managed to set off the blast. "There may have been some laxity," Chidambaram said.

He described the explosion as a "low to medium intensity blast" but strong enough to throw debris up to 30 feet (9 meters) away.

Hundreds of worshippers flocked Wednesday to Sheetla Ghat at dawn to offer prayers, said Surendra Srivastav, a police spokesman in Uttar Pradesh's capital Lucknow.

In March 2006, twin bombings blamed on a Pakistan-based Islamic militant group tore through a train station and a temple in Varanasi, killing 20 people.

Ayodhya, Varanasi, and Lucknow are potentially explosive places with a mixed population of Hindus and Muslims. The demolition of the Babri mosque sparked nationwide riots that killed 2,000 people and shook the foundations of India's claim to be a multiethnic, secular democracy.