The government's chief law officer has warned the US that it must think again on plans to conduct military tribunals on suspects held at Camp Delta.

Attorney general Lord Goldsmith told a Paris audience that US plans for the trial of detainees held at Guantanamo Bay are unacceptable.

"While we must be flexible and be prepared to countenance some limitation of fundamental rights if properly justified and proportionate, there are certain principles on which there can be no compromise," he said.

"Fair trial is one of those – which is the reason we in the UK have been unable to accept that the US military tribunals proposed for those detained at Guantanamo Bay offer sufficient guarantees of a fair trial in accordance with international standards."

Despite warning that the treatment of terror suspects must be just, he conceded that the threat posed by al Qaeda raised new issues for law makers.

"It is now clear that it is organised and executed through an international network of cells and different organisations able to call on help and assistance from many determined people in different countries," Goldsmith added.

"This diffuse and globalised structure presents enormous challenges to the law enforcement agencies of individual countries."

He also signalled that ministers are "grappling with how we should confront the difficult question of striking the balance between protection of our security and the protection of fundamental rights and freedoms".

And he conceded that the nature of the new terror threat has led to a re-evaluation of rights and responsibilities.

"The first point to make is that the law recognises that there is a balance to be struck between the rights of the individual and the rights of society," Goldsmith said.

"While the terrorist does not forfeit his fundamental rights, the law does recognise that those rights can be restricted or derogated from in particular circumstances.

"Rights are not only one-way. And it is not only the rights of suspected persons which are important.

"The rights and liberties of other citizens are important too.

"Let us not forget that terrorism, by its methods and aims, has the potential to render nugatory all the individual rights which we all hold so dear."