At least 13 small bombs exploded in the Indian city of Ahmedabad yesterday, killing at least five people and wounding 55, a day after another set of blasts in the country's IT hub, officials said.
On Friday, eight bombs exploded in quick succession in the southern IT city of Bangalore, killing at least one person and wounding six others.
Yesterday's blasts were in Ahmedabad's crowded old city dominated by its Muslim community. One was left in a metal tiffin box, used to carry food, another apparently left on a bicycle.
"This has been done by some terrorist group which wants to destabilise the country," the central government's junior home minister Shriprakash Jaiswal told the Sahara news channel.
One television channel showed a bus with its side blown up, shattered windows and the roof half-destroyed. Another showed a dead dog lying beside a blown-up bicycle.
"The bus had just started when the blast happened," P. K Pathak, a retired insurance official who was travelling in nearby bus, told Reuters.
"Many people standing on the exit door fell down. There was fire and smoke all over. We got down from our bus and rushed to help them."
Ahmedabad is the main city in the communally sensitive and relatively wealthy western state of Gujarat, 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.
Both states targeted in the bomb attacks are ruled by the Hindu-nationalist Bharatiya Janata Party and are among the country's fastest-growing.
Suspicion is falling on Islamist militants intent on destabilising India by fanning tensions between Hindus and Muslims, and police were deployed in Ahmedabad yesterday to maintain calm.
India has suffered a wave of bombings in recent years, with targets ranging from mosques and Hindu temples to trains.
It is unusual for any group to claim responsibility, but India says it suspects militant groups from Pakistan and Bangladesh are behind many of the attacks.
"The government had received a threat e-mail and we are probing into it," local state government Home Minister Amit Shah told Reuters.