BEIJING (Reuters) - China has detained a Swedish national who worked with human rights lawyers on suspicion of endangering state security, a rights group said on Wednesday, describing the charges as “baseless”.

Peter Dahlin was taken into custody on Jan. 4, the group said, amid a growing crackdown on rights lawyers and foreign groups working on legal reform. Rights groups say the crackdown aims to rein in dissent, but the Chinese government denies this.

Dahlin, 35, is the co-founder of the Chinese Urgent Action Working Group, which promotes human rights and rule of law in China by supporting public interest lawyers and academics, among others.

“China Action is dedicated to promoting human rights within the existing legal framework of the People’s Republic of China and has only ever advocated non-violent, informed reliance on Chinese law,” the group said in its statement.

“In spite of this, Peter has been arbitrarily detained on spurious accusations.”

The Swedish Foreign Ministry confirmed the man had been detained. A spokesman for the Swedish embassy in Beijing said it had been in touch with Chinese authorities about meeting him, but gave no further details.

Chinese authorities had not yet allowed embassy officials or others to contact him, Dahlin’s group said, adding that he suffers from Addison’s Disease and requires medication.

Hong Lei, a spokesman for China’s Foreign Ministry, said he did not know about the detention.

China has detained or formally jailed several foreign nationals in recent years, sometimes over their proximity to what it perceives as sensitive information.

“This action is just the most recent in an extra-legal or illegal pattern of apprehending civil rights lawyers,” said Lionel Jensen, an associate professor at the University of Notre Dame who researches Chinese nationalism. “These are dark days in China, to be sure.”

China formally arrested several Chinese human rights lawyers on suspicion of subverting state power after months of secret detention, one of their colleagues said on Tuesday.

At least two Japanese citizens were arrested on suspicion of espionage last year and a Canadian couple was arrested in 2014 amid a crackdown on foreign Christian groups along the country’s sensitive border with North Korea.