WASHINGTON, Jan 22: The United States said on Tuesday it was not yet clear if an attack on the American Center in Kolkata, was a terror assault targeted at its interests or the result of a grievance against local police.

“As far as who exactly was responsible for this we don’t know at this point,” said State Department spokesman Richard Boucher.

Four unidentified gunmen on motorcycles opened fire on the center on Tuesday morning, killing four policemen and injuring 20 people.

Boucher said that US officials were aware of reports that police and local newspapers had received claims that the attack was targeted at police officers guarding the center in revenge for actions by West Bengal authorities against a group on the India- Bangladesh border.

Several anonymous calls claimed responsibility for the assault.

Boucher said Secretary of State Colin Powell spoke to both President Musharraf and Indian foreign minister Jaswant Singh following the Kolkata attack on Tuesday.