July 30 (Bloomberg) -- Indian police defused a bomb in the nation's diamond-polishing center of Surat, extending a series of failed attacks and blasts that have killed at least 52 people in less than a week.

The device was discovered in the Varacha area hours after Gujarat Chief Minister Narendra Modi visited, said R.M.S. Brar, commissioner of police in the western Indian city. Schools, colleges, shopping malls, parks and public places were closed, he said. Modi offered a 5.1 million rupee ($120,000) reward for information leading to arrests of terrorists in the state.

At least 20 devices hidden in cars and garbage cans have been discovered since 23 bombs tore through bus stations and markets in Bangalore and Ahmedabad last week. Television images of police gathering clues and neutralizing devices lead hourly news bulletins as an Islamist group claiming responsibility for the blasts in Ahmedabad threatened further attacks.

``In spite of our efforts, some places were overlooked,'' Brar said. ``People are bringing them to the notice of the police.''

Sixteen bombs exploded in Ahmedabad within 20 minutes late on July 26, a day after seven bombs tore through India's technology hub of Bangalore, killing two. On July 27, two vehicles filled with explosives were found and defused in Surat, Gujarat Health Minister Jaynarayan Narmadasankar Vyas said.

Attacks Threatened

A little-known Islamist group, calling itself the ``Indian Mujahideen,'' claimed responsibility for the Ahmedabad blasts and threatened more attacks, according to an e-mail received by some newspapers and television channels, including Star News.

The group claimed that the attack was in revenge for violence in Gujarat between Hindus and Muslims in 2002 in which almost 2,000 people were killed.

The modus operandi of blasts in the last two years has been the same, Modi said in Surat. ``This is one sort of proxy war'' waged by enemies of the country.

The government has previously blamed terrorist attacks on organizations linked to foreign powers, without offering evidence or making arrests. Local media often blame the attacks on groups backed by Pakistan or Bangladesh, without identifying the security officials who provided the information.

Security has been increased in states including Gujarat, Karnataka and Kerala, apart from the cities of New Delhi, Mumbai, Chennai, Bangalore and Hyderabad.

The investigation is moving in the ``right direction,'' Vyas said today by phone from Ahmedabad, declining to disclose further information. ``Any declaration prematurely will only help those miscreants.''

To contact the reporters on this story: Bibhudatta Pradhan in New Delhi at bpradhan@bloomberg.net.

Last Updated: July 30, 2008 05:38 EDT