Beirut: More than two dozen rights groups on Thursday called for the release of Syrian human rights lawyer Khalil Maatouq, two years after his "enforced disappearance" in Damascus.
The appeal was co-signed by 26 human rights organisations, including Amnesty International, Human Rights Watch, Reporters Without Borders and several regional watchdogs.
Maatouq, executive director of the Syrian Centre for Legal Studies and Research, and his assistant Mohammad Zaza disappeared two years ago as they were heading to their office in the Syrian capital.
"It is believed that they were arrested at a government security checkpoint solely due to his legitimate and peaceful work in human rights," said the joint statement.
"Multiple reports have confirmed that the two men are being held by the Syrian authorities, who appear to move them among various detention facilities in Damascus, including the `Palestine Branch`, a detention centre run by military intelligence," it added.
The rights organisations called on the Syrian government to "immediately and unconditionally" free Maatouq and Zaza.
"Syrian authorities deny that the men are in custody, placing them at particular risk of torture or other ill-treatment and even extra-judicial execution," the statement said.
The rights watchdogs said that Maatouq suffers from "advanced lung disease" and has "severe breathing difficulties."
"Reports from former detainees indicate that he is in extremely poor health, a source of great concern for his family, his lawyers and the organisations."
Maatouq built a reputation for defending political prisoners in Syria and has been described by Amnesty International as a "prisoner of conscience".
Hope that Maatouq and his colleague would be released ran high after Syrian President Bashar al-Assad issued a decree in June to free prisoners, after securing a new term in a controversial election.
But lawyers said that fewer than 1,500 people were set free, not many of them political activists.
Activists say tens of thousands of people are being held by the Syrian authorities, many of them arrested arbitrarily since the outbreak of the revolt against Assad in March 2011.