The headquarters of investment firm Goldman Sachs towers over smaller buildings in New York in this 11 Dec. 2006 file photo

U.S. authorities are investigating threats against investment bank Goldman Sachs, but are downplaying their credibility.

Goldman Sachs officials in New York say letters sent from New York City to several newspapers across the nation warned, "Hundreds will die. We are inside. You cannot stop us."

The letters are signed AQUSA, a possible reference to al-Qaida.

The FBI is quoted as saying the threats do not appear to be very credible, but that the agency and Goldman Sachs take all such matters seriously.

Some information for this report was provided by Reuters.