A human rights group says their Swedish co-founder has been detained by Chinese authorities on suspicion of endangering state security.

Peter Dahlin's detention comes as China intensifies a crackdown on civil society to snuff out any potential opposition to the ruling Communist Party.

China Urgent Action Working Group says 35-year-old Dahlin was detained on Jan. 3 on his way to Beijing's main airport, where he was due to fly to Thailand via Hong Kong. His Chinese girlfriend also has disappeared.

The group says Dahlin suffers from a medical condition that needs daily medication.

The Swedish Embassy in Beijing confirmed that a 35-year-old citizen had been detained in China and says it is investigating.

China has been cracking down on human rights activists, lawyers and bloggers.