Indian Prime Minister Manmohan Singh has appealed for calm after a series of explosions killed at least 46 people in two Indian cities.
India's major cities were later put on alert amid fears of more attacks.
At least 16 bombs exploded in the western city of Ahmedabad in Gujarat state yesterday, killing at least 45 people and wounding 161, a day after another set of blasts in Bangalore killed a woman.
Two more unexploded bombs were found today in the city of Surat, one of the world's biggest diamond-polishing centres, located in Gujarat state.
A little-known group called the Indian Mujahideen claimed responsibility for yesterday's attack. The same group said it carried out bomb attacks that killed 63 people in the western city of Jaipur in May.
It is unusual for any group to claim responsibility, but India says it suspects militant groups from Pakistan and Bangladesh are behind a wave of bombings in recent years, with targets ranging from mosques and Hindu temples to trains.
'The entire nation, including major metro cities in India, have been put on high alert and they have been asked to step up security in vital installations,' a home ministry spokesman said.
In New Delhi, police used loudspeakers and distributed leaflets in crowded market places, warning people to watch out for unclaimed baggage and suspicious objects. Police guarded Hindu temples in the eastern city of Kolkata.
There were two separate series of bombings in Ahmedadad, the first near busy market places. A second quick succession of bombs went off 25 minutes later around a hospital, where at least six people died, police said. All were detonated with timers.
Two doctors were killed in the hospital in a blast in which at least one bomb was tied onto a gas cylinder. The other bombs were in Ahmedabad's crowded old city, dominated by its Muslim community. Many of the bombs were packed into metal tiffin boxes, used to carry food, and stuffed with ball-bearings. Some were left on bicycles.
Police found two unexploded bombs in Ahmedabad today. The state government has ordered the closure of all shops, cinemas and markets and has told people to stay indoors.
Ahmedabad is the main city in the communally sensitive and relatively wealthy western state of Gujarat, which was scene of deadly riots in 2002 in which 2,500 people are thought to have died, most of them Muslims killed by rampaging Hindu mobs.
Ahmedabad and Bangalore are in states ruled by the Hindu-nationalist Bharatiya Janata Party and are among the country's fastest-growing.
