Mumbai, Aug 20 - The US Federal Bureau of Investigation (FBI) has filed a case in connection with the 26/11 Mumbai terror attacks, in which six American nationals were among those killed, and has also interrogated some Pakistani nationals, an FBI agent told a Mumbai Special Court here Thursday.

The FBI's special agent said a case has been registered in Los Angeles for the terror attacks, as the agency registers a case whenever any US national is killed in any foreign country.

'I am the investigation officer in the case which was registered soon after the attacks,' he told Special Judge M.L. Tahilyani.

The FBI agent cannot be named, according to the special court's order.

When cross-examined by state appointed defence lawyer S.G. Abbas Kazmi, representing Pakistani terror accused Mohammed Ajmal Amir Kasab, the FBI agent declined to reveal the names of the Pakistanis who have been interrogated and said investigations were in still progress.

He also told Special Public Prosecutor Ujjwal Nikam that the FBI had received a letter related to the 26/11 attacks from the 37th Additional Metropolitan Court of Mumbai Feb 19.