Washington, Aimed at blocking lawyers' access to a high-profile detainee at Guantanamo Bay, Cuba, the US government called the interrogation techniques "national security secrets" whose revelation could "cause extremely grave damage", the Washington Post reported Saturday. The US government said the prisoners at secret CIA prisons must not be allowed to talk about the interrogation methods used on them - even to their lawyers, the Post reported. A lawyer at a firm that represents many prisoners at Guantanamo Bay, Cuba, has sought access to Majid Khan, who was transferred to Guantanamo along with 14 other prisoners from secret sites in September. The lawyer said the government was "attempting to misuse its classification authority" by claiming that all of the detainees' experiences were top-secret and could not be discussed. In documents filed in a US court last week, the government expressed concern that allowing prisoners who had been held at CIA prisons to have contact with lawyers would jeopardize the secrecy of the interrogation techniques used on them. A CIA official writes in the court filing that allowing the prisoners access to the lawyers "poses an unacceptable risk of disclosure." US President George W Bush insists the CIA programme has been essential to fighting terrorism since the Sep 11, 2001 Al Qaeda attacks on New York and Washington, which killed nearly 3,000 people. Since the attacks, the CIA had held dozens of suspects at secret locations around the world. Among them are Khalid Sheikh Mohammed, the plot's alleged mastermind, and suspected top Al Qaeda operatives Ramzi Binalshibh and Abu Zubaydah. Bush announced in September that detainees held for years in CIA custody had been transferred to the US military base at Guantanamo to face prosecution.