Story highlights Sweden's embassy to China confirms arrest of "Swedish citizen in his mid-30s"

Man's detention comes amid mass arrests of lawyers and human rights activists across China

Hong Kong (CNN) A Swedish human rights activist has been detained in China amid an ongoing crackdown on lawyers and NGOs.

According to colleagues, Peter Jesper Dahlin was detained "on suspicion of endangering state security" on January 4.

"A Swedish citizen in his mid-30s has been detained in China," a spokesman for the Swedish Embassy in Beijing told CNN, adding that consular staff were currently investigating the matter.

Dahlin worked for the Chinese Urgent Action Group, which "undertakes rapid response assistance for rights defenders in need" and provides legal aid and training across China, according to its website.

The Chinese Ministry of Foreign Affairs did not respond to a request for comment.