People stand around the site of an explosion in Ahmadabad. (Ajit Solanki/Associated Press)

India's president and prime minister have appealed for calm after a deadly series of explosions in the western city of Ahmedabad, apparently intended to inflame relations between Hindus and Muslims.

India has suffered periodic spasms of sectarian violence since it gained independence from Britain in 1947 as the subcontinent was partitioned between a mainly Hindu India and a mainly Muslim Pakistan.

In Ahmedabad, 17 separate blasts, all within an hour, killed at least 45 people and wounded more than 160 in Saturday. A little-known group calling itself the Indian Mujahideen claimed responsibility.

The bombs are thought to have been crudely made devices hidden in boxes and on bicycles, the BBC reported. Some bombs in a second wave of explosions targeted the hospitals where the injured were being taken, it said.

Ahmedabad, in Gujarat state, is a crowded and historic city that in 2002 was the scene of riots that killed about 1,000 people, most of them Muslims.

That violence was triggered by a fire that killed 60 passengers on a train packed with Hindu pilgrims. Although the cause of the blaze was unclear, Hindu extremists blamed the deaths on Muslims and rampaged through Muslim neighbourhoods.

The group that claimed responsibility for the Saturday attack sent an e-mail to a number of Indian television news stations minutes before the blasts began, the Associated Press reported.

"In the name of Allah, the Indian Mujahideen strike again! Do whatever you can, within 5 minutes from now, feel the terror of Death!" the message said.

There was doubt about the authenticity of the e-mail, partly because it was sent from a French Yahoo account but was written in English by a person who signed it Guru al-Hindi, or Teacher of Indians, using a blend of Arabic and Hindi considered unusual among South Asia's Muslims, the news agency said.

India's president, Pratibha Patil, and its prime minister, Manmohan Singh, joined the leader of the Opposition, Lal Krishna Advani, in condemning the blasts as an insensate act of violence and appealing for peace, the Times of India reported.

The latest attacks came a day after seven synchronized small bombs shook Bangalore, India's high-tech hub, killing two people and wounding at least five others. On Saturday, police found and defused an eighth bomb near a popular shopping mall in Bangalore.