China detains Swedish human rights worker Peter Dahlin

China has detained a Swedish human rights worker in Beijing, amid a crackdown on defence lawyers.

Peter Dahlin is believed to be the first foreign national detained in connection with the drive.

The foreign ministry said Mr Dahlin, who co-founded a group offering legal aid to Chinese citizens, is suspected of harming the national interest.

Since July, nearly 300 people in China's legal community have faced police questioning or detention.

Peter Dahlin's Chinese girlfriend is also missing and is thought to be in police custody.

Earlier, Chinese Urgent Action Working Group (China Action) said Mr Dahlin had been detained on 4 January while en route to the airport.

Swedish officials have said they are looking into the detention of one of their citizens in China.

On Tuesday several lawyers were said to have been charged with "subversion".

China Action describes itself as a legal aid organisation. It provides assistance to uncertified lawyers who provide legal aid in rural areas, as well as directly aids disadvantaged groups and individuals who have experienced rights violations.

It has told reporters that Mr Dahlin, 35, was detained on suspicion of "endangering state security".

"Peter has been arbitrarily detained on spurious accusations," a spokesman was quoted as saying by AFP news agency.

The group also says officials were denying all access to Mr Dahlin who is suffering from Addison's Disease, a rare defect of the adrenal gland, which needs daily medication.

Sweden's foreign affairs ministry has tweeted that a 35-year-old male citizen has been detained in China. "Our embassy is looking into this and has requested to visit him," it said.

Reuters news agency quoted Hong Lei, a Chinese foreign ministry spokesman, as saying that he did not know about the detention.

On Tuesday, seven human rights lawyers and their associates who have been missing since last summer were formally arrested and charged with "subversion", according to their friends and relatives.

Two more human rights lawyers - Wang Yu and husband Bao Longjun - were formally arrested on subversion charges on Wednesday, a lawyer said.

Mr Dahlin is not the only Swedish citizen thought to be in Chinese custody.

Another Swedish citizen, China-born Gui Minhai, is also missing in connection to a suspected crackdown on a Hong Kong bookshop known for publishing and carrying books critical of the Chinese government.

In July, the Chinese authorities launched what appeared to be an orchestrated campaign, when more than 280 human rights lawyers and activists - along with their associates - were summoned, detained or just disappeared. The arrests have been widely seen as the state's attempts to stifle dissent.