The group's statement prompted prosecutors to file a contempt petition last month against the group. The prosecution's filing said the group raised "biased, baseless, utterly false, fabricated and ill-motivated" allegations involving the trial process.
The U.S. ambassador in Bangladesh, Dan Mozena, expressed his concern last month over the prosecutors' move. He said an organization like Human Rights Watch has "a critical role to play."
The prosecutors' petition names the group's board of directors, its director for the Asia region, Brad Adams, and his associate Storm Tiv.
There was no immediate response from Human Rights Watch. It said last month that it was not in a position to respond because it had not received any official notification of the prosecutor's contempt petition.
Prime Minister Sheikh Hasina's government is holding the war crimes trials despite protests from the main opposition Bangladesh Nationalist Party and its main ally Jamaat-e-Islami party.