Human rights group Amnesty International says it is deeply concerned for the safety of two terror suspects who were deported from the UK.
The men felt their only option was to return home, lawyers said
The organisation claims the Algerian men - known only as Q and K - were sent back to their homeland "despite the risk that they would be tortured".
The two men were flown from the UK on 20 January, having dropped their appeals against deportation orders.
Amnesty has claimed the men are being held by Algeria's military police.
Q and K were first arrested in Britain under the anti-terrorism act of 2001, but in December 2004 the Law Lords ruled that detention without charge under this act was unlawful and the two men were released.
Amnesty says the case against the men was never disclosed to them.
The organisation believes both were arrested by Algeria's military police, the DRS, on Wednesday and have been in custody every since.
It says the DRS has a well documented record of torture and that Britain knowingly deported the men despite this risk.
Amnesty International UK director, Kate Allen said: "We are deeply concerned that these men are at risk of torture.
"The DRS is known to particularly target people suspected of having information about terrorism.
"As these men have been labelled 'suspected international terrorists' by the UK authorities, they were always at risk of torture and should never have been returned to Algeria."
Radical Algerian terror cells
Earlier, the Home Office said it was not the first time that suspected terrorists had been deported to Algeria - two men were sent back in June last year.
The men were among a group of 27 foreigners held because of fears that they are a threat to national security.
Some of the men, who cannot be named due to a court order, have been held without trial for more than four years.
The men were all suspected terrorists and some were believed to have connections to radical Algerian terror cells.
Their lawyers said the suspects could no longer bear indefinite detention and felt their only option was to agree to go back home.
Human rights campaigners claims that they will be tortured have been denied by Algeria and the British government says it has assurances that the men will not be mistreated.
The government said it intended to deport the other men who have also withdrawn their appeals against deportation as soon as possible, a spokeswoman added.