Updated 8:59 PM ET
HYDERABAD, India A pair of bombs exploded in a crowded shopping area in the southern Indian city of Hyderabad, killing at least 13 people and wounding scores of others in the worst bombing in the country in more than a year, officials said.
The blasts occurred about two minutes apart at around 7 p.m. Thursday outside a movie theater and a bus station, police said. Storefronts were shattered, motorcycles covered in debris, and food and plates from a roadside restaurant were scattered on the ground near a tangle of dead bodies. Passersby rushed the wounded out of the area.
"This is a dastardly attack, the guilty will not go unpunished," Prime Minister Manmohan Singh said. He appealed to the public to remain calm.
The bombs were attached to two bicycles about 150 meters (500 feet) apart in Dilsukh Nagar district, Home Minister Sushilkumar Shinde told reporters in New Delhi. The district is a usually crowded shopping area near a residential neighborhood.
When asked if the government had any suspects, Shinde responded: "We have to investigate."
Andhra Pradesh state Home Minister P. Sabita Reddy said 11 people died on the spot in the two blasts and another two succumbed to their injuries in hospital on Thursday night.
She said another 78 people were injured and hospitalized in the city.
Top state police officer V. Dinesh Reddy said improvised explosive devices with nitrogen compound were used in Thursday's blasts.
Mahesh Kumar, a 21-year-old student, was heading home from a tutoring class when a bomb went off.
"I heard a huge sound and something hit me, I fell down, and somebody brought me to the hospital," said Kumar, who suffered shrapnel wounds.
Hyderabad, a city of 10 million in the state of Andhra Pradesh, is a hub of India's information technology industry and has a mixed population of Muslims and Hindus.
"This (attack) is to disturb the peaceful living of all communities in Andhra Pradesh," said Kiran Kumar Reddy, the state's chief minister.
The explosions were the first major bomb attack to hit India since a September 2011 blast outside the High Court in New Delhi killed 13 people. The government has been heavily criticized for its failure to arrest the masterminds behind previous bombings.
Officials from the National Investigation Agency and commandos of the National Security Guards arrived from New Delhi to Hyderabad to help with the investigation.
The United States, whose Secretary of State John Kerry was meeting Thursday in Washington with Indian Foreign Secretary Ranjan Mathai, condemned the attack.
"The United States stands with India in combating the scourge of terrorism and we also prepared to offer any and all assistance Indian authorities may need," State Department spokeswoman Victoria Nuland told a news briefing.
Rana Banerji, a former security official, said India remains vulnerable to such attacks because there is poor coordination between the national government and the states. Police reforms are also moving very slowly and the quality of intelligence gathering is poor, he said.
"The concept of homeland security should be made effective, on a war footing," he said.
Rajnath Singh, the president of main opposition Bharatiya Janata Party, demanded a thorough probe into the blasts. His party called for a general strike in the state on Friday.
India has been in a state of alert since Mohammed Afzal Guru, a Kashmiri, was hanged in a New Delhi jail nearly two weeks ago. Guru had been convicted of involvement in a 2001 attack on India's Parliament that killed 14 people, including five gunmen.
Many in Indian-ruled Kashmir believe Guru did not receive a fair trial, and the secrecy with which the execution was carried out fueled anger in a region where anti-India sentiment runs deep.