A Swedish human rights activist arrested in China earlier this month for allegedly posing a threat to national security has returned home after his expulsion, he said on Tuesday.

‘I'm back in Sweden now. I arrived this morning, after various delays but I'm in my hometown now with my parents,’ said Peter Dahlin of the Chinese Urgent Action Working Group.

‘I'm happy to be back but three of my colleagues and close friends are still being held,’ he told Swedish Radio.

Dahlin, who suffers from Addison's disease, said China had released him for ‘medical and diplomatic reasons’.

The 35-year-old disappeared on January 4 as he prepared to board a flight to Thailand.

He appears to have been caught up in a crackdown on human rights lawyers.

Dahlin's group has said it offered training to lawyers who have tried to use the tightly controlled judiciary to redress apparent government abuses.

Chinese state broadcaster CCTV last week aired footage of a dazed and harried-looking Dahlin apologising to China for his alleged actions, which officials said had ‘threatened state security’.

The Chinese government confirmed on Tuesday it had expelled him from the country.

‘We have deported him,’ Hua Chunying, a foreign ministry spokeswoman, told a regular press briefing.

Dahlin's Chinese girlfriend, who had also been held, ‘has been released and there are no charges against her,’ the activist said.

The Swede's detention came as China considers a new law to control the activities of foreign non-governmental organisations, which has raised widespread concern among rights groups.

The ruling Communist Party has in recent months stepped up its scrutiny of NGOs, while state media has warned of ‘hostile foreign forces’ said to be using them to foment revolution.

Authorities also launched a sweeping crackdown on human rights attorneys in July, detaining more than 130 legal staff across the country. This month at least 10 were formally arrested on charges related to ‘state subversion’ after being held in secret for six months.

- 'Intimidation and fear' -

Observers said Dahlin's case was intended to send a warning to NGOs.

‘I can see why the PRC released him now,’ Jerome Cohen, a law professor at New York University, wrote in a blog post, using shorthand for the country's official name, the People's Republic of China.

‘The authorities made their point, spreading intimidation and fear throughout both the domestic and foreign legal and NGO worlds.’

Rights groups echoed these sentiments, with Nicholas Bequelin, Amnesty International's East Asia director, writing on Twitter: ‘China has sent the clearest signal yet that it intends to cut domestic NGOs from foreign funding.’

Another Swedish national, Hong Kong bookseller Gui Minhai, disappeared from Thailand late last year before reappearing on Chinese national television in police custody.

Gui, who was born in China, confessed to a drink-driving offence on the mainland dating back years and said he did not want Stockholm to interfere with his case.

He was rumoured to be among those preparing a tell-all book about the love life of President Xi Jinping.

Beijing only rarely accuses foreigners of endangering state security, a crime which can involve a heavy sentence.

But as Beijing has tightened social controls in recent years, it has sought to blame ‘foreign forces’ for domestic woes, ranging from undermining Chinese values to a recent explosion in labour protests.

Swedish Foreign Minister Margot Wallstrom, who had protested to China about the detention of the two Swedish nationals, welcomed Dahlin's release.

‘This is the result of close contacts between the Swedish foreign ministry and Chinese representatives,’ she said in a statement on Monday.