A Swedish human rights worker is in detention in Beijing, accused of "harming the national interest."
The Chinese girlfriend of Peter Dahlin is also thought to be in custody, the BBC reports.
Dahin's NGO, the Chinese Urgent Action Working Group (or simply China Action), said the 35-year-old was first held on Jan. 4. Sweden's foreign ministry said in a tweet that it was a aware a 35-year-old national was being held and "Our embassy is looking into this and has requested to visit him."
China Action, described as a legal aid organization helping people who have experienced rights violations, says all access has been denied to Dahlin. The BBC reports that he suffers from Addison's Disease and needs medication on a daily basis.
Another Swedish national, Gui Minhai, is also thought to be in custody in China. The co-owner of a Hong Kong based publishing firm that specializes in books critical of Chinese leaders, he was last seen in October on holiday in Thailand. Gui is one of five people connected to Mighty Current Media to have vanished mysteriously in recent months.