Indian television channels reported that they had received a claim of responsibility from a little-known group calling itself the "Indian Mujahidin".
"We have heard of the Indian Mujahidin in an earlier blast but nobody confirmed whether this organisation exists or if it's a cover up for any other organisation which is creating trouble in India," Shakeel Ahmed, India's minister of state for home affairs and spokesperson for the Indian national congress, told Al Jazeera.
"People who want to disrupt the peace of this country are behind these blasts."
The Press Trust of India (PTI) news agency said nine people had died of their injuries overnight, and around 162 others are still being treated for injuries on Sunday.
The blasts on Saturday follow seven almost simultaneous bombings in across the city of Bangalore the previous day, which left at least two people dead.
Multiple blasts
Police said that the first explosion was reported at around 6pm local time (12:30 GMT) on a bridge in Ahmedabad, which saw bloody clashes between Hindus and Muslims in 2002.
Many of the bombs were placed in busy areas of the city, including a railway station and a diamond market.
Some devices were attached to bicycles, while one appeared to have been detonated on a bus.
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| Some devices were attached to bicycles in different parts of Ahmedabad [AFP] |
Officials and medical staff said that many of the injured had been hit by flying nuts, bolts and ball bearings packed into the bombs.
Al Jazeera's Todd Baer, reporting from New Delhi, said that officials were saying that the blasts were "low-intensity" bombings, similar to those which occured in Bangalore.
Sriprakash Jaiswal, a junior home minister, was critical that the attacks had come despite security being heightened after the Bangalore blasts.
"This is very unfortunate and we are surprised that despite a high security alert sounded yesterday after the bomb attacks in Bangalore, the blasts occurred today in Ahmedabad. We are shocked," he told reporters in New Delhi.
"It seems there is a lack of co-ordination between [federal] intelligence agencies and people involved in the policing."
Manmohan Singh, the Indian prime minister, condemned the attack and urged Ahmedabad residents to remain calm, his office in New Delhi said.
Narendra Modi, the chief minister of Gujarat state, said: "The land of Mahatma Gandhi has been bloodied by terrorists whom we shall not spare."
Suspicions
India's home ministry said that it suspected "a small militant group" was behind the attacks in Bangalore.
"Special squads have been formed to find out who is behind the blasts. We have not got any conclusive leads yet," MR Pujar, Bangalore's additional commissioner of police, said on Saturday.
Islamist groups in Pakistan and Bangladesh have been blamed for previous attacks in India.
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| The attack was the second to hit a BJP-ruled state within 48 hours [AFP] |
Ajai Sahni, a security analyst from India's Institute of Conflict Management, said: "This seems to be within a very long established battle and we have been seeing such blasts in intervals of a few weeks to three months, almost regularly for the past three to four years, somewhere or other in the country."
"One or a combination of a small group of terrorist organisations is in all probability involved in these blasts as well," he told Al Jazeera.
"Controlling interests are the same. However, the executing groups may or may not be the same, but the overall umbrella of organisations who are the handlers are basically the same group of Pakistan-based groups backed by the inter-service intelligence of Pakistan.
"All past major incidents that we have seen have pointed to control on Pakistani soil and there is no reason to believe that they are not connected through one single objective," Sahni said.
In May, eight bombs, many strapped to bicycles, ripped through a crowded shopping area in the western city of Jaipur, killing at least 63 people and injuring hundreds more.