Four gunmen riding two motorcycles sprayed automatic gunfire outside the US government cultural centre on Tuesday, leaving five dead and 16 wounded.
Draped in shawls, the attackers rode up to the American centre in the heart of the eastern metropolis of Calcutta at 6.30 am local time (0100 GMT), shot at police officers and fled, said Sujoy Chakraborty, the Calcutta police commissioner.
The wounded included state police officers and at least one private security guard working at the building.
No one has yet claimed responsibility for the attack but it is believed that a radical islamic group may be responsible.
The attack occurred when the police officers on the night shift were changing guard, spent AK–47 bullets were found at the site.
In the Indian capital, a high alert was issued at the US Embassy and other American institutions in New Delhi.
Joint Commissioner of Police Suresh Roy said there had been intelligence reports of a possible strike to US establishments in India, as part of the "unprecedented threat" during India's Republic Day celebrations on Saturday.
"We have tightened the entire security arrangement at the US Embassy and all US establishments. A general alert has been sounded," Roy said. "This is a serious matter. We are keeping a close watch."
In a terrorist attack in the heart of the Indian capital on 13 December, five armed suicide attackers forced their way into the Indian Parliament and killed nine government workers before being killed themselves.
The American Centre, one of the two US government buildings in Calcutta, houses a popular library spread over two floors, the embassy's public affairs office, a press section and a wing for cultural programs.
The centre is one of the landmarks of Calcutta, the capital of the communist–run West Bengal state. Anti–American protests by communists and labor unions are often held there and hundreds of students visit its library each day.
Security has been tightened in recent months at the American Embassy, consulate buildings across the country and other offices to prevent possible attacks by Islamic guerrillas fighting to separate the Himalayan region of Kashmir from Indian control.
The attack occurred as US Ambassador at Large Francis X Taylor, President George W. Bush's coordinator for counterterrorism, was in New Delhi to discuss ways to prevent just such violence. FBI Director Robert Mueller was also in the Indian capital to hold talks with Indian officials.Reuse content