A five-year battle for classified files on Australia's knowledge of the Balibo massacre in East Timor has hit another obstacle.

In October 1975 Channel Seven journalist Greg Shackleton sent his final report from East Timor.

Within hours he and four other Australian newsmen were murdered by Indonesian forces at Balibo.

A Canberra academic has been trying to force the Australian Secret Intelligence Service to release records about its activity in East Timor in the 1970s.

The director-general of ASIS has asked the Attorney-General to step in.

