Amnesty International on Thursday called on the Moroccan authorities to immediately and unconditionally release three Sahrawi activists set to face trial following their visit to refugee camps in Algeria run by the Polisario Front.
The trial of Brahim Dahane, Ali Salem Tamek and Ahmed Nasiri, begins on Friday in the Court of First Instance, Casablanca. All have been accused of "undermining (Morocco's) internal security".
Amnesty International said it considers the three men to be prisoners of conscience.
Yahdih Ettarouzi, Saleh Labihi, Dakja Lashgar, and Rachid Sghir who were provisionally released, are also on trial on the same charges.
"It is simply unacceptable that the Moroccan authorities are prosecuting these seven individuals, who include human rights defenders and former victims of enforced disappearance, for freely and openly visiting refugee camps and meeting with Polisario Front officials," said Malcolm Smart, Amnesty International's director for the Middle East and North Africa.
"Brahim Dahane, Ali Salem Tamek and Ahmed Nasiri have been incarcerated for over a year for actions that amount to no more than peacefully exercising their right to freedom of expression and association.
"The charges against them are clearly politically-motivated and they should be dropped immediately. These prosecutions should not proceed."
Initially charged with "undermining (Morocco's) external security", and its "territorial integrity", the case was under prolonged investigation by Morocco's Military Court for nearly 12 months before being passed to civilian courts.
All three of those still being held have been confined at Salé Prison, near Rabat, since 16 October 2009. They were arrested on 8 October 2009 at Mohammed V airport in Casablanca following their return from refugee camps in Tindouf, Algeria.
Brahim Dahane, Ali Salem Tamek and Ahmed Nasiri are among a number of Sahrawi activists who have faced harassment and intimidation for publicly expressing their views on the self-determination of Western Sahara, which Morocco annexed in 1975, and for documenting human rights violations committed by the Moroccan authorities.
Brahim Dahane said in a statement received via his family: "For a quarter of a century, we have been victims of arbitrary arrests, enforced disappearance and harassment as a result of our views, expressed peacefully."
The Polisario Front calls for the independence of Western Sahara and runs a self-declared government in exile, the Sahrawi Arab Democratic Republic (SADR).
"The Moroccan authorities should not treat peaceful political expression as a national security issue, as they are doing in this case," said Malcolm Smart.
"Instead, the Moroccan authorities must live up to their human rights obligations and demonstrate their commitment to the rule of law by upholding the right to freedom of expression and association for all those peacefully supporting the self-determination of Western Sahara."
The Polisario Front has also clamped down on dissent. On 21 September 2010, Mustafa Salma, a Polisario Front member, was arrested by Polisario Front officials on his way to the Tindouf camps after having publicly supported autonomy for Western Sahara under Moroccan rule.
Despite also being a civilian, his case was first referred to military trial, and he was accused of undermining the security of SADR. According to the Sahara Press Service, he was released on 6 October, but his relatives have had no news from him since his arrest, raising fears about his safety.