Students at Columbia University were shocked by the incident

Police are investigating the incident as a possible hate crime.

Columbia students and staff have expressed their shock and surprise at the incident - which occurred at the university's teachers college.

The incident recalls a case in Jena, Louisiana, where white students hung a noose in a tree after a black student asked if he too could enjoy its shade.

Columbia University has not identified the professor who found the noose on Tuesday, but students say she teaches a class on racial justice.

Teachers college president Susan Fuhrman sent an e-mail to students and faculty members condemning "this hateful act".

Student Mary Owens told the Associated Press news agency: "It's really, really disturbing."

Professor Arlene Ackerman, who teaches at the college, said she was "shocked and stunned".

'Double standards'

Nooses are reviled by many as symbols of lynchings that were once common in the southern US.

In the Jena case racial tensions were sparked after three nooses were found hanging from a tree in the school yard, the day after a black pupil asked if he too could sit under it.

That incident resulted in three white students being suspended from school, but not prosecuted.

In a later incident six black teenagers at the school, who became known as the Jena Six, were charged with attempted murder after they allegedly attacked a white pupil at the school, although these charges were subsequently reduced.

The white teenage victim was beaten unconscious and had a badly swollen face, but was able to attend a school event the same evening.

The case provoked one of the biggest civil rights protests in recent years with demonstrators criticising what they said was a double standard of prosecution for blacks and whites.