Activists say the health of a prominent Syrian rights lawyer believed to be in government custody for more than eight months is deteriorating and has called for his release.

Khalil Maatouk, 53, was abducted while driving to his office in Damascus in October and he has been incommunicado since.

The Britain-based Syrian Observatory for Human Rights said Thursday it has learned that Maatouk is being held in a Syrian intelligence detention facility. It says Maatouk, who has lung disease, is suffering from deteriorating health.

The Observatory relies on a network of activists on the ground in Syria to gather information about the two-year conflict.

Maatouk has tracked and reported on the detention of activists since before the uprising against President Bashar Assad began in March 2011.