LONDON,  (AFP) - Britain was working to move up to 90 suspected insurgents being held at its main base in Afghanistan, Defence Secretary Philip Hammond said Wednesday, as lawyers claimed they were possibly being detained unlawfully.

British lawyers representing eight of the men being held at Camp Bastion in the southern province of Helmand claim their cases could amount to internment.

Hammond said the detainees in the "temporary holding facility" included people suspected of attacking British troops who will be passed on to the Afghan authorities, but that their transfers had been held up.

He dismissed claims that the facility was secret as "patently ridiculous" and said the British parliament had been informed of the detentions. Hammond said Britain would normally expect to be holding around 20 Afghans at Camp Bastion at any one time, but concerns about a particular facility they might be transferred to had created a hold-up in the system.

"These are people suspected of murdering British troops, of facilitating or planting or being involved with IEDs (improvised explosive devices)," the minister said.

"Our attention was drawn to some concerns around one particular Afghan facility. We were unable to obtain cast-iron guarantees that the prisoners that we were transferring wouldn't be transferred into that facility.

"And so I decided last November that we had to stop transfers until we had sorted that out and got a safe pathway."

Hammond said he hoped to restart transfers within days. "That will resolve the conundrum and allow us to get these detainees transferred into an Afghan facility with proper overwatch and a proper judicial process," he said.

The Ministry of Defence said transfers to the Afghan facility had been halted after the emergence of "new evidence that suggested a risk of mistreatment of detainees".

It added: "Since then we have been working with the Afghan authorities to identify a safe route for the transfer of detainees into the Afghan judicial system."

British lawyers acting for the men said their clients had been held for up to 14 months without charge.

They compared the potential impact of the revelation that more than 80 men were detained there to when the public became aware of the US-run Guantanamo Bay prison.

Phil Shiner, of Public Interest Lawyers, said: "This is a secret facility that's been used to unlawfully detain or intern up to 85 Afghans that they've kept secret, that parliament doesn't know about, that courts previously when they have interrogated issues like detention and internment in Afghanistan have never been told about -- completely off the radar.

"It is reminiscent of the public's awakening that there was a Guantanamo Bay. And people will be wondering if these detainees are being treated humanely and in accordance with international law." British forces are normally allowed to hold suspects detained in Afghanistan for 96 hours, but they can be held for longer in "exceptional circumstances", such as to obtain critical intelligence.