Syrian author Ali al-Abdullah,
The 61-year-old author, who served a sentence of two-and-a-half years from December 2007 to June 2010 for calling for democracy, had been set to be released in June 2010.
But he remained in custody to face a new trial over comments he made while in prison on Syrian-Lebanese relations, and alleged electoral fraud in Iran's 2009 election, the groups said.
Abdullah is one of 12 signatories of the 2005 "Damascus Declaration," which called for Syria to move towards democracy.
All 12 were sentenced to two-and-a-half years in jail by the Damascus Criminal Court for "undermining the image of the state" and "spreading false news."
The rights groups expressed their "extreme concern at the severity with which the Syrian authorities treat political activists" and demanded "the dropping of all charges against Mr Abdullah and his immediate release."
The groups that issued the statement were the Syrian Observatory for Human Rights, the Syrian League for the Defence of Human Rights, the National Organisation for Human Rights in Syria and the Arab Organisation for Human Rights in Syria.
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But he remained in custody to face a new trial over comments he made while in prison on Syrian-Lebanese relations, and alleged electoral fraud in Iran's 2009 election, the groups said.
Abdullah is one of 12 signatories of the 2005 "Damascus Declaration," which called for Syria to move towards democracy.
All 12 were sentenced to two-and-a-half years in jail by the Damascus Criminal Court for "undermining the image of the state" and "spreading false news."
The rights groups expressed their "extreme concern at the severity with which the Syrian authorities treat political activists" and demanded "the dropping of all charges against Mr Abdullah and his immediate release."
The groups that issued the statement were the Syrian Observatory for Human Rights, the Syrian League for the Defence of Human Rights, the National Organisation for Human Rights in Syria and the Arab Organisation for Human Rights in Syria.
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