KOLKATA, Jan 22: Four unidentified armed men on motorcycles opened fire outside the American Center here on Tuesday, killing five policemen and injuring 20 people.

Police said the four men rode up at 6:30am (0100 GMT) to the Center located on one of eastern Kolkata’s main thoroughfares, and started spraying bullets indiscriminately, before fleeing.

Two anonymous calls to the media suggested that separate groups had claimed responsibility for the attack: the Harkat-ul-Jihad Islami — a militant group fighting Indian occupation in Kashmir — and the Asif Raza Commandos, blamed for a spate of kidnappings in Kolkata, including that of a prominent businessman last year.

Four police guards were killed on the spot while another succumbed to injuries in hospital. Twenty other police guards were injured, with a civilian and a private security guard.

“This was definitely an attack on the American Center by terrorists of some group or the other,” Kolkata police chief Sujoy Chakraborty said.

The building, which is several kilometres from the US consulate, houses a library, press and commercial office, and is staffed by mainly Indian nationals and a handful of American diplomats.

“There were no American citizens injured and there were no US consulate staff in the Center at the time of the incident,” said Gordon Duguid, chief information officer at the US embassy in New Delhi.

He declined to speculate on the group or motive behind the attack.

The shooting came less than six weeks after an attack on parliament in New Delhi triggered a dangerous escalation in military tensions with Pakistan.

Security had been stepped up at all US diplomatic buildings following the Sept 11 terrorist attacks in New York and Washington.

The attack came as the guards at the Center were changing duty, said Mr Chakraborty, adding the attackers had driven up with automatic weapons hidden under their large winter shawls.

They fired up to 50 rounds at the security personnel standing outside the Center’s main gate.

“People just started dropping to the ground,” said taxi driver Mahesh Ghosh who witnessed the shooting.

The state of West Bengal was put on maximum alert, while the area around the American Center was cordoned off by the police.

Robert Mueller, director of the Federal Bureau of Investigation, and Admiral Thomas Wilson, the chief of the US Defence Intelligence Agency, are both currently visiting India.

Following talks in New Delhi with his Indian counterpart, P.C. Sharma, Mr Mueller refused to comment on the shooting, although Mr Sharma said it was discussed during their meeting.

There are four American Centers in India, in the cities of Bombay, Kolkata, Chenai and New Delhi.—Agencies